diff --git a/lib/shared/dm-ops/process-dm-ops.js b/lib/shared/dm-ops/process-dm-ops.js
index 2cab04f4c..ac8b7ec5d 100644
--- a/lib/shared/dm-ops/process-dm-ops.js
+++ b/lib/shared/dm-ops/process-dm-ops.js
@@ -1,128 +1,173 @@
 // @flow
 
 import _groupBy from 'lodash/fp/groupBy.js';
 import * as React from 'react';
 import uuid from 'uuid';
 
 import { dmOpSpecs } from './dm-op-specs.js';
 import type { DMOperationSpecification } from './dm-op-utils.js';
 import { useLoggedInUserInfo } from '../../hooks/account-hooks.js';
 import { useGetLatestMessageEdit } from '../../hooks/latest-message-edit.js';
 import { useDispatchWithMessageSource } from '../../hooks/ops-hooks.js';
 import { mergeUpdatesWithMessageInfos } from '../../reducers/message-reducer.js';
 import { usePeerToPeerCommunication } from '../../tunnelbroker/peer-to-peer-context.js';
 import type { MessageSourceMetadata } from '../../types/db-ops-types.js';
 import {
   type DMOperation,
   processDMOpsActionType,
   queueDMOpsActionType,
 } from '../../types/dm-ops.js';
+import type { RawThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
+import { threadTypes } from '../../types/thread-types-enum.js';
+import type { LegacyRawThreadInfo } from '../../types/thread-types.js';
 import { updateTypes } from '../../types/update-types-enum.js';
 import { useSelector } from '../../utils/redux-utils.js';
+import { messageSpecs } from '../messages/message-specs.js';
+import { updateSpecs } from '../updates/update-specs.js';
 
 function useProcessDMOperation(): (
   dmOp: DMOperation,
   metadata: ?MessageSourceMetadata,
 ) => Promise<void> {
   const fetchMessage = useGetLatestMessageEdit();
   const threadInfos = useSelector(state => state.threadStore.threadInfos);
 
   const utilities = React.useMemo(
     () => ({
       fetchMessage,
       threadInfos,
     }),
     [fetchMessage, threadInfos],
   );
 
   const dispatchWithMessageSource = useDispatchWithMessageSource();
   const loggedInUserInfo = useLoggedInUserInfo();
   const viewerID = loggedInUserInfo?.id;
   return React.useCallback(
     async (dmOp: DMOperation, metadata: ?MessageSourceMetadata) => {
       if (!viewerID) {
         console.log('ignored DMOperation because logged out');
         return;
       }
       const processingCheckResult = dmOpSpecs[dmOp.type].canBeProcessed(
         dmOp,
         viewerID,
         utilities,
       );
       if (!processingCheckResult.isProcessingPossible) {
         if (processingCheckResult.reason.type === 'missing_thread') {
           dispatchWithMessageSource(
             {
               type: queueDMOpsActionType,
               payload: {
                 operation: dmOp,
                 threadID: processingCheckResult.reason.threadID,
                 timestamp: Date.now(),
               },
             },
             metadata,
           );
         }
         return;
       }
       const { rawMessageInfos, updateInfos } = await dmOpSpecs[
         dmOp.type
       ].processDMOperation(dmOp, viewerID, utilities);
 
       const { rawMessageInfos: allNewMessageInfos } =
         mergeUpdatesWithMessageInfos(rawMessageInfos, updateInfos);
       const messagesByThreadID = _groupBy(message => message.threadID)(
         allNewMessageInfos,
       );
+
+      const updatedThreadInfosByThreadID: {
+        [string]: RawThreadInfo | LegacyRawThreadInfo,
+      } = {};
+      for (const threadID in messagesByThreadID) {
+        updatedThreadInfosByThreadID[threadID] = threadInfos[threadID];
+      }
+      for (const update of updateInfos) {
+        const updatedThreadInfo = updateSpecs[
+          update.type
+        ].getUpdatedThreadInfo?.(update, updatedThreadInfosByThreadID);
+        if (
+          updatedThreadInfo &&
+          updatedThreadInfo?.type === threadTypes.THICK_SIDEBAR
+        ) {
+          updatedThreadInfosByThreadID[updatedThreadInfo.id] =
+            updatedThreadInfo;
+        }
+      }
+
       for (const threadID in messagesByThreadID) {
+        const repliesCountIncreasingMessages = messagesByThreadID[
+          threadID
+        ].filter(message => messageSpecs[message.type].includedInRepliesCount);
+        if (repliesCountIncreasingMessages.length > 0) {
+          const threadInfo = updatedThreadInfosByThreadID[threadID];
+          const repliesCountIncreaseTime = Math.max(
+            repliesCountIncreasingMessages.map(message => message.time),
+          );
+          updateInfos.push({
+            type: updateTypes.UPDATE_THREAD,
+            id: uuid.v4(),
+            time: repliesCountIncreaseTime,
+            threadInfo: {
+              ...threadInfo,
+              repliesCount:
+                threadInfo.repliesCount + repliesCountIncreasingMessages.length,
+            },
+          });
+        }
+
         const messagesFromOtherPeers = messagesByThreadID[threadID].filter(
           message => message.creatorID !== viewerID,
         );
         if (messagesFromOtherPeers.length === 0) {
           continue;
         }
         // We take the most recent timestamp to make sure that updates older
         // than it won't flip the status to read.
         const time = Math.max(
           messagesFromOtherPeers.map(message => message.time),
         );
         updateInfos.push({
           type: updateTypes.UPDATE_THREAD_READ_STATUS,
           id: uuid.v4(),
           time,
           threadID,
           unread: true,
         });
       }
 
       dispatchWithMessageSource(
         {
           type: processDMOpsActionType,
           payload: {
             rawMessageInfos,
             updateInfos,
           },
         },
         metadata,
       );
     },
-    [viewerID, utilities, dispatchWithMessageSource],
+    [viewerID, utilities, dispatchWithMessageSource, threadInfos],
   );
 }
 
 function useProcessAndSendDMOperation(): (
   dmOperationSpecification: DMOperationSpecification,
 ) => Promise<void> {
   const processDMOps = useProcessDMOperation();
   const { sendDMOperation } = usePeerToPeerCommunication();
 
   return React.useCallback(
     async (dmOperationSpecification: DMOperationSpecification) => {
       await processDMOps(dmOperationSpecification.op);
       await sendDMOperation(dmOperationSpecification);
     },
     [processDMOps, sendDMOperation],
   );
 }
 
 export { useProcessDMOperation, useProcessAndSendDMOperation };