diff --git a/lib/components/modal-overlay.react.js b/lib/components/modal-overlay.react.js
--- a/lib/components/modal-overlay.react.js
+++ b/lib/components/modal-overlay.react.js
@@ -24,7 +24,7 @@
   } = props;
 
   const overlayRef = React.useRef<?HTMLDivElement>();
-  const firstClickRef = React.useRef<?HTMLElement>(null);
+  const firstClickRef = React.useRef<?EventTarget>(null);
 
   React.useLayoutEffect(() => {
     if (overlayRef.current) {
@@ -32,12 +32,15 @@
     }
   }, []);
 
-  const onBackgroundMouseDown = React.useCallback(event => {
-    firstClickRef.current = event.target;
-  }, []);
+  const onBackgroundMouseDown = React.useCallback(
+    (event: SyntheticEvent<HTMLDivElement>) => {
+      firstClickRef.current = event.target;
+    },
+    [],
+  );
 
   const onBackgroundMouseUp = React.useCallback(
-    event => {
+    (event: SyntheticEvent<HTMLDivElement>) => {
       if (
         event.target === overlayRef.current &&
         firstClickRef.current === overlayRef.current
@@ -49,7 +52,7 @@
   );
 
   const onKeyDown = React.useCallback(
-    event => {
+    (event: SyntheticKeyboardEvent<HTMLDivElement>) => {
       if (event.key === 'Escape') {
         onClose();
       }
diff --git a/lib/components/modal-provider.react.js b/lib/components/modal-provider.react.js
--- a/lib/components/modal-provider.react.js
+++ b/lib/components/modal-provider.react.js
@@ -34,7 +34,7 @@
     () => setModals(oldModals => oldModals.slice(0, -1)),
     [],
   );
-  const pushModal = React.useCallback(newModal => {
+  const pushModal = React.useCallback((newModal: React.Node) => {
     const key = getUUID();
     setModals(oldModals => [...oldModals, [newModal, key]]);
     return key;
diff --git a/lib/hooks/child-threads.js b/lib/hooks/child-threads.js
--- a/lib/hooks/child-threads.js
+++ b/lib/hooks/child-threads.js
@@ -14,7 +14,7 @@
 import { childThreadInfos } from '../selectors/thread-selectors.js';
 import { threadInChatList } from '../shared/thread-utils.js';
 import threadWatcher from '../shared/thread-watcher.js';
-import type { ThreadInfo } from '../types/thread-types.js';
+import type { ThreadInfo, RawThreadInfo } from '../types/thread-types.js';
 import { useDispatchActionPromise } from '../utils/action-utils.js';
 import { useSelector } from '../utils/redux-utils.js';
 
@@ -40,7 +40,13 @@
   }, [childThreads, predicate]);
 
   const filterSubchannels = React.useCallback(
-    thread => subchannelIDs.has(thread?.id),
+    (thread: ?(ThreadInfo | RawThreadInfo)) => {
+      const candidateThreadID = thread?.id;
+      if (!candidateThreadID) {
+        return false;
+      }
+      return subchannelIDs.has(candidateThreadID);
+    },
     [subchannelIDs],
   );
   const allSubchannelsList = useFilteredChatListData(filterSubchannels);
diff --git a/lib/shared/state-sync/entries-state-sync-spec.js b/lib/shared/state-sync/entries-state-sync-spec.js
--- a/lib/shared/state-sync/entries-state-sync-spec.js
+++ b/lib/shared/state-sync/entries-state-sync-spec.js
@@ -75,10 +75,12 @@
     (state: AppState) => state.entryStore.entryInfos,
     entryInfos => ({
       ...entriesStateSyncSpec,
-      getInfoHash: id => hash(entryInfos[`${ashoatKeyserverID}|${id}`]),
-      getAllInfosHash: calendarQuery =>
+      getInfoHash: (id: string) =>
+        hash(entryInfos[`${ashoatKeyserverID}|${id}`]),
+      getAllInfosHash: (calendarQuery: CalendarQuery) =>
         getEntryInfosHash(entryInfos, calendarQuery),
-      getIDs: calendarQuery => getEntryIDs(entryInfos, calendarQuery),
+      getIDs: (calendarQuery: CalendarQuery) =>
+        getEntryIDs(entryInfos, calendarQuery),
     }),
   ),
 });
diff --git a/lib/shared/state-sync/threads-state-sync-spec.js b/lib/shared/state-sync/threads-state-sync-spec.js
--- a/lib/shared/state-sync/threads-state-sync-spec.js
+++ b/lib/shared/state-sync/threads-state-sync-spec.js
@@ -59,7 +59,7 @@
       state.integrityStore.threadHashingStatus === 'completed',
     (threadHashes, threadHashingComplete) => ({
       ...threadsStateSyncSpec,
-      getInfoHash: id => threadHashes[`${ashoatKeyserverID}|${id}`],
+      getInfoHash: (id: string) => threadHashes[`${ashoatKeyserverID}|${id}`],
       getAllInfosHash: threadHashingComplete
         ? () => combineUnorderedHashes(values(threadHashes))
         : () => null,
diff --git a/lib/shared/state-sync/users-state-sync-spec.js b/lib/shared/state-sync/users-state-sync-spec.js
--- a/lib/shared/state-sync/users-state-sync-spec.js
+++ b/lib/shared/state-sync/users-state-sync-spec.js
@@ -56,7 +56,7 @@
     (state: AppState) => state.userStore.userInfos,
     userInfos => ({
       ...usersStateSyncSpec,
-      getInfoHash: id => hash(userInfos[id]),
+      getInfoHash: (id: string) => hash(userInfos[id]),
       getAllInfosHash: () =>
         combineUnorderedHashes(Object.values(userInfos).map(hash)),
       getIDs: () => Object.keys(userInfos),