diff --git a/lib/hooks/relationship-hooks.js b/lib/hooks/relationship-hooks.js
--- a/lib/hooks/relationship-hooks.js
+++ b/lib/hooks/relationship-hooks.js
@@ -87,7 +87,7 @@
   );
   const createNewThickThread = useNewThickThread();
 
-  const filterUsersSupportingThickThreads = useUsersSupportThickThreads();
+  const mapUsersSupportingThickThreads = useUsersSupportThickThreads();
 
   const updateRelationshipsAndSendRobotext = React.useCallback(
     async (action: RelationshipAction, userIDs: $ReadOnlyArray<string>) => {
@@ -98,10 +98,13 @@
         return {};
       }
       const usersSupportingThickThreads =
-        await filterUsersSupportingThickThreads(userIDs);
+        await mapUsersSupportingThickThreads(userIDs);
       const planForUsers = new Map<string, RobotextPlanForUser>();
       for (const userID of userIDs) {
-        if (!usersSupportingThickThreads.has(userID)) {
+        if (usersSupportingThickThreads.get(userID) === undefined) {
+          throw new Error('Cannot fetch user identity');
+        }
+        if (!usersSupportingThickThreads.get(userID)) {
           planForUsers.set(userID, { plan: 'send_to_thin_thread' });
           continue;
         }
@@ -220,7 +223,7 @@
     [
       viewerID,
       updateRelationships,
-      filterUsersSupportingThickThreads,
+      mapUsersSupportingThickThreads,
       pendingToRealizedThreadIDs,
       sendRobotextToThickThread,
       userInfos,
diff --git a/lib/hooks/thread-search-hooks.js b/lib/hooks/thread-search-hooks.js
--- a/lib/hooks/thread-search-hooks.js
+++ b/lib/hooks/thread-search-hooks.js
@@ -106,7 +106,7 @@
       filterAndSetUserResults(
         identitySearchUsers.map(search => ({
           ...search,
-          supportThickThreads: userIDsSupportingThickThreads.has(search.id),
+          supportThickThreads: !!userIDsSupportingThickThreads.get(search.id),
         })),
       );
     })();
diff --git a/lib/hooks/user-identities-hooks.js b/lib/hooks/user-identities-hooks.js
--- a/lib/hooks/user-identities-hooks.js
+++ b/lib/hooks/user-identities-hooks.js
@@ -7,18 +7,18 @@
 
 function useUsersSupportThickThreads(): (
   userIDs: $ReadOnlyArray<string>,
-) => Promise<$ReadOnlySet<string>> {
+) => Promise<$ReadOnlyMap<string, ?boolean>> {
   const findUserIdentities = useFindUserIdentities();
   const auxUserInfos = useSelector(state => state.auxUserStore.auxUserInfos);
 
   return React.useCallback(
     async (userIDs: $ReadOnlyArray<string>) => {
-      const usersSupportingThickThreads = new Set<string>();
+      const usersSupportingThickThreads = new Map<string, ?boolean>();
 
       const usersNeedingFetch = [];
       for (const userID of userIDs) {
         if (auxUserInfos[userID]?.deviceList) {
-          usersSupportingThickThreads.add(userID);
+          usersSupportingThickThreads.set(userID, true);
         } else {
           usersNeedingFetch.push(userID);
         }
@@ -27,7 +27,11 @@
         const { identities } = await findUserIdentities(usersNeedingFetch);
         for (const userID of usersNeedingFetch) {
           if (identities[userID]) {
-            usersSupportingThickThreads.add(userID);
+            usersSupportingThickThreads.set(userID, true);
+          } else if (identities[userID] === undefined) {
+            usersSupportingThickThreads.set(userID, undefined);
+          } else {
+            usersSupportingThickThreads.set(userID, false);
           }
         }
       }
diff --git a/lib/shared/thread-utils.js b/lib/shared/thread-utils.js
--- a/lib/shared/thread-utils.js
+++ b/lib/shared/thread-utils.js
@@ -1788,7 +1788,7 @@
         return;
       }
       const result = await usersSupportThickThreads([userInfo.id]);
-      setSupportThickThreads(result.has(userInfo.id));
+      setSupportThickThreads(!!result.get(userInfo.id));
     })();
   }, [userInfo, usersSupportThickThreads]);
 
diff --git a/native/chat/message-list-container.react.js b/native/chat/message-list-container.react.js
--- a/native/chat/message-list-container.react.js
+++ b/native/chat/message-list-container.react.js
@@ -299,7 +299,7 @@
         );
         setAllUsersSupportThickThreads(
           userInfoInputArray.every(userInfo =>
-            usersSupportingThickThreads.has(userInfo.id),
+            usersSupportingThickThreads.get(userInfo.id),
           ),
         );
       })();
diff --git a/web/chat/chat-thread-composer.react.js b/web/chat/chat-thread-composer.react.js
--- a/web/chat/chat-thread-composer.react.js
+++ b/web/chat/chat-thread-composer.react.js
@@ -115,7 +115,7 @@
           allUsersSupportThickThreads:
             user.id === viewerID
               ? true
-              : usersSupportingThickThreads.has(user.id),
+              : !!usersSupportingThickThreads.get(user.id),
         });
         dispatch({
           type: updateNavInfoActionType,
diff --git a/web/utils/thread-utils.js b/web/utils/thread-utils.js
--- a/web/utils/thread-utils.js
+++ b/web/utils/thread-utils.js
@@ -88,7 +88,7 @@
       );
       setAllUsersSupportThickThreads(
         selectedUserInfos.every(userInfo =>
-          usersSupportingThickThreads.has(userInfo.id),
+          usersSupportingThickThreads.get(userInfo.id),
         ),
       );
     })();