diff --git a/src/App.jsx b/src/App.jsx
index 2a72ce1..93e7356 100644
--- a/src/App.jsx
+++ b/src/App.jsx
@@ -1,4 +1,5 @@
 import { PureComponent, lazy, Suspense } from 'react';
+import Alert from '@mui/material/Alert';
 import Box from '@mui/material/Box';
 import CircularProgress from '@mui/material/CircularProgress';
 import authAutomat from './automats/authAutomat';
@@ -34,7 +35,13 @@ class App extends PureComponent {
   }
 
   componentDidMount() {
-    this.unsubscribe = authAutomat.subscribe(this, ['status', 'user', 'hasAuth', 'hasCompany']);
+    this.unsubscribe = authAutomat.subscribe(this, [
+      'status',
+      'user',
+      'hasAuth',
+      'hasCompany',
+      'retryNotification',
+    ]);
   }
 
   componentWillUnmount() {
@@ -42,7 +49,7 @@ class App extends PureComponent {
   }
 
   render() {
-    const { status, user, hasAuth, hasCompany } = this.state;
+    const { status, user, hasAuth, hasCompany, retryNotification } = this.state;
     const isAuthed = Boolean(hasAuth ?? (status === 'authed' && user));
     const isCompanySelected = Boolean(hasCompany ?? (isAuthed && user?.selectedCompanyId != null));
 
@@ -51,12 +58,29 @@ class App extends PureComponent {
         <Box
           sx={{
             display: 'flex',
+            flexDirection: 'column',
             alignItems: 'center',
             justifyContent: 'center',
             minHeight: 'var(--df-vh, 100vh)',
             bgcolor: 'background.default',
+            gap: 2.5,
+            p: 2,
           }}
         >
+          {retryNotification ? (
+            <Alert
+              severity="warning"
+              variant="outlined"
+              sx={{
+                maxWidth: 480,
+                alignItems: 'center',
+                bgcolor: 'background.paper',
+                boxShadow: 1,
+              }}
+            >
+              {retryNotification}
+            </Alert>
+          ) : null}
           <CircularProgress />
         </Box>
       );
diff --git a/src/automats/authAutomat.js b/src/automats/authAutomat.js
index bbef708..8ea8d6c 100644
--- a/src/automats/authAutomat.js
+++ b/src/automats/authAutomat.js
@@ -33,6 +33,7 @@ import { auth, company, number as numberApi } from '../api';
  * @property {'loading'|'anon'|'authed'} status Current authentication lifecycle state.
  * @property {boolean} hasAuth True when the session has a valid authenticated user.
  * @property {boolean} hasCompany True when `hasAuth` is true AND a company is selected.
+ * @property {string|null} retryNotification Message indicating a pending retry (e.g. 502 Bad Gateway).
  */
 
 /** Emitted after an authenticated session has been established. */
@@ -49,11 +50,24 @@ const initialState = {
     status: 'loading',
     hasAuth: false,
     hasCompany: false,
+    retryNotification: null,
 };
 
 let emit = () => { };
 
 // #region helpers
+/**
+ * Detects whether an error represents an HTTP 502 Bad Gateway response.
+ *
+ * @param {any} err
+ * @returns {boolean}
+ */
+export function is502BadGateway(err) {
+    if (!err) return false;
+    if (Number(err.status) === 502) return true;
+    const msg = String(err.message || '');
+    return /502|bad\s*gateway/i.test(msg);
+}
 /**
  * Registers the application-level dispatcher used for authentication events.
  *
@@ -108,6 +122,7 @@ function buildAuthState(user, status, extra = {}) {
         status,
         hasAuth,
         hasCompany,
+        retryNotification: null,
         ...extra,
     };
 }
@@ -126,52 +141,86 @@ function syncSse(state) {
         }
     }
 }
+
+function applySession(nextSession) {
+    const googleClientId =
+        nextSession.googleClientId ?? authAutomat.state.googleClientId;
+
+    if (!nextSession.user) {
+        if (authAutomat.state.status !== 'authed') {
+            const nextState = authAutomat.setState(
+                buildAuthState(null, 'anon', { googleClientId, retryNotification: null })
+            );
+            syncSse(nextState);
+        } else {
+            authAutomat.setState({ googleClientId, retryNotification: null });
+        }
+        return nextSession;
+    }
+
+    const user = mergeUser(authAutomat.state.user, nextSession.user);
+    const nextState = authAutomat.setState(
+        buildAuthState(user, 'authed', { googleClientId, retryNotification: null })
+    );
+    syncSse(nextState);
+    emit({ type: AUTH_SESSION_ESTABLISHED });
+    return nextSession;
+}
 // #endregion
 
 let authAutomat;
+let inFlightBootstrap = null;
 
 const actions = {
     // #region bootstrapSession
     // MARK: calls auth.me from ../api
     /**
      * Restores an existing session or requests it from the authentication API.
+     * Retries automatically every 5 seconds if a 502 Bad Gateway is received.
      *
      * @param {{user?: AuthUser|null, googleClientId?: string|null}|null} [session]
      *   Optional preloaded session.
      * @returns {Promise<Object>} Resolved session response.
      */
     async bootstrapSession(session) {
-        try {
-            const nextSession = session ?? await auth.me();
-            const googleClientId =
-                nextSession.googleClientId ?? authAutomat.state.googleClientId;
-
-            if (!nextSession.user) {
-                if (authAutomat.state.status !== 'authed') {
-                    const nextState = authAutomat.setState(
-                        buildAuthState(null, 'anon', { googleClientId })
-                    );
-                    syncSse(nextState);
-                } else {
-                    authAutomat.setState({ googleClientId });
-                }
-                return nextSession;
-            }
-
-            const user = mergeUser(authAutomat.state.user, nextSession.user);
-            const nextState = authAutomat.setState(
-                buildAuthState(user, 'authed', { googleClientId })
-            );
-            syncSse(nextState);
-            emit({ type: AUTH_SESSION_ESTABLISHED });
-            return nextSession;
-        } catch (error) {
-            if (authAutomat.state.status === 'loading') {
-                const nextState = authAutomat.setState(buildAuthState(null, 'anon'));
-                syncSse(nextState);
-            }
-            throw error;
+        if (session) {
+            return applySession(session);
         }
+
+        if (inFlightBootstrap) {
+            return inFlightBootstrap;
+        }
+
+        inFlightBootstrap = (async () => {
+            let attempt = 0;
+            while (true) {
+                try {
+                    const nextSession = await auth.me();
+                    return applySession(nextSession);
+                } catch (error) {
+                    if (is502BadGateway(error)) {
+                        attempt++;
+                        authAutomat.setState({
+                            retryNotification: `Server nicht erreichbar (502 Bad Gateway) – erneuter Versuch in 5s…${attempt > 1 ? ` (Versuch ${attempt})` : ''}`,
+                        });
+                        await new Promise((resolve) => setTimeout(resolve, 5000));
+                        continue;
+                    }
+
+                    if (authAutomat.state.status === 'loading') {
+                        const nextState = authAutomat.setState(
+                            buildAuthState(null, 'anon', { retryNotification: null })
+                        );
+                        syncSse(nextState);
+                    }
+                    throw error;
+                }
+            }
+        })().finally(() => {
+            inFlightBootstrap = null;
+        });
+
+        return inFlightBootstrap;
     },
     // #endregion
 
@@ -302,6 +351,7 @@ export const selectHasAuth = () => Boolean(authAutomat.state.hasAuth);
 export const selectHasCompany = () => Boolean(authAutomat.state.hasCompany);
 export const selectSelectedCompanyId = () =>
     authAutomat.state.hasCompany ? authAutomat.state.user?.selectedCompanyId ?? null : null;
+export const selectRetryNotification = () => authAutomat.state.retryNotification;
 
 /**
  * Re-reads `GET /api/auth/me` from the server.
@@ -312,7 +362,7 @@ export const selectSelectedCompanyId = () =>
  * @returns {Promise<{user: AuthUser|null, googleClientId: string|null}>} Session.
  */
 export function bootstrapAuthMe() {
-    return auth.me();
+    return authAutomat.actions.bootstrapSession();
 }
 // #endregion
 
diff --git a/src/components/AuthBootstrap.jsx b/src/components/AuthBootstrap.jsx
index 5e2bfc8..e232ec8 100644
--- a/src/components/AuthBootstrap.jsx
+++ b/src/components/AuthBootstrap.jsx
@@ -1,7 +1,7 @@
 import { Component } from 'react';
 import { enqueueSnackbar } from 'notistack';
 import { notifyError } from '../utils/notify';
-import authAutomat, { bootstrapAuthMe } from '../automats/authAutomat';
+import authAutomat, { is502BadGateway } from '../automats/authAutomat';
 
 let sessionBootstrapped = false;
 
@@ -10,15 +10,16 @@ class AuthBootstrap extends Component {
     if (sessionBootstrapped) return;
     sessionBootstrapped = true;
 
-    bootstrapAuthMe()
+    authAutomat.actions.bootstrapSession()
       .then((session) => {
-        if (session.forbidden) {
+        if (session?.forbidden) {
           enqueueSnackbar(session.message, { variant: 'warning' });
         }
-        return authAutomat.actions.bootstrapSession(session);
       })
       .catch((err) => {
-        notifyError(err);
+        if (!is502BadGateway(err)) {
+          notifyError(err);
+        }
       });
   }