Cannot join a channel as admin using the Web app

Description:

Using the Web version of RocketChat, as an admin, I can't join some channels : when I click the blue button bottom-right, the bell rings, the channel view crashes, and on refresh a message "[user] has joined the channel" appears but the button is still there. Same for sending a message : it gets sent, but the Web app does not understand I've joined.

This issue affects only old admins on our instance. The instance has been updated several times, the last was 3.6.3 -> 3.8.3.
All browsers tested (Firefox, Chrome, Kiwi, Chromium).

No problem from the android app.

Steps to reproduce:

1. As an old admin, hit Ctrl-K and find a public channel you're not in
2. Click the join button / send a message
3. Hear the bell, see the channel view become white
4. You're in the channel according to the chat history, but not for the Web client

Expected behavior:

Join the channel.

Actual behavior:

The blank page :

After refresh, I've officially joined this channel several times... still not in.

Server Setup Information:

• Version of Rocket.Chat Server: 3.8.3
• Operating System: Android / Ubuntu
• Deployment Method: kubernetes
• Number of Running Instances: 1
• DB Replicaset Oplog:
• NodeJS Version: v12.18.4
• MongoDB Version: 3.6.12

Client Setup Information

• Desktop App or Browser Version:
• Operating System:

Relevant logs:

No JS error or log in the browser console when the error happens.

Start by reproducing the join and send-message flows in the Rocket.Chat Web client with an old admin account, following the Ctrl-K steps and checking the browser console. No source file or test is named in the report; done means the channel view remains usable and the client reflects the successful join without requiring a refresh.