diff --git a/lib/reducers/keyserver-reducer.js b/lib/reducers/keyserver-reducer.js
--- a/lib/reducers/keyserver-reducer.js
+++ b/lib/reducers/keyserver-reducer.js
@@ -75,20 +75,29 @@
       keyserverInfos,
     };
   } else if (action.type === setNewSessionActionType) {
-    const { keyserverID } = action.payload;
-    if (action.payload.sessionChange.cookie !== undefined) {
+    const { keyserverID, sessionChange } = action.payload;
+    if (!state.keyserverInfos[keyserverID]) {
+      if (sessionChange.cookie?.startsWith('user=')) {
+        console.log(
+          'received sessionChange with user cookie, ' +
+            `but keyserver ${keyserverID} is not in KeyserverStore!`,
+        );
+      }
+      return state;
+    }
+    if (sessionChange.cookie !== undefined) {
       state = {
         ...state,
         keyserverInfos: {
           ...state.keyserverInfos,
           [keyserverID]: {
             ...state.keyserverInfos[keyserverID],
-            cookie: action.payload.sessionChange.cookie,
+            cookie: sessionChange.cookie,
           },
         },
       };
     }
-    if (action.payload.sessionChange.cookieInvalidated) {
+    if (sessionChange.cookieInvalidated) {
       state = {
         ...state,
         keyserverInfos: {
diff --git a/web/redux/redux-setup.js b/web/redux/redux-setup.js
--- a/web/redux/redux-setup.js
+++ b/web/redux/redux-setup.js
@@ -164,12 +164,21 @@
       storeOperations,
     );
   } else if (action.type === setNewSessionActionType) {
-    const { keyserverID } = action.payload;
+    const { keyserverID, sessionChange } = action.payload;
+    if (!state.keyserverStore.keyserverInfos[keyserverID]) {
+      if (sessionChange.cookie?.startsWith('user=')) {
+        console.log(
+          'received sessionChange with user cookie, ' +
+            `but keyserver ${keyserverID} is not in KeyserverStore!`,
+        );
+      }
+      return state;
+    }
 
     if (
       invalidSessionDowngrade(
         oldState,
-        action.payload.sessionChange.currentUserInfo,
+        sessionChange.currentUserInfo,
         action.payload.preRequestUserState,
         keyserverID,
       )
@@ -188,7 +197,7 @@
           ...state.keyserverStore.keyserverInfos,
           [keyserverID]: {
             ...state.keyserverStore.keyserverInfos[keyserverID],
-            sessionID: action.payload.sessionChange.sessionID,
+            sessionID: sessionChange.sessionID,
           },
         },
       },