If you start responding in a thread and enter another chat and then return, the send icon disappears

Description:

If you start responding in a thread and enter another chat and then return, the previously typed text is saved, but the send icon disappears. Instead, icons for downloading an attachment or voicemail are sometimes displayed (screenshot 1), and sometimes a blue "Follow" button (screenshot 2)

Steps to reproduce:

1. start typing the answer in the thread
2. there is an icon for sending a message (screenshot 1)
3. do not send a reply but go to another chat
4. return to thread
5. the text is saved but there is no send icon, instead of it there are two other icons (screenshot 2)
6. sometimes a blue "Follow" button is displayed instead of two icons (screenshot 3)

Expected behavior:

5. the text is saved and there is an icon for sending a message

Actual behavior:

5. the text is saved but there is no send icon, instead of it there are two other icons

Server Setup Information:

• Version of Rocket.Chat Server: 3.13.2
• Operating System:
• Deployment Method:
• Number of Running Instances:
• DB Replicaset Oplog:
• NodeJS Version:
• MongoDB Version:

Client Setup Information

• Desktop App or Browser Version: Google Chrome 90.0.4430.93
• Operating System: macOS Big Sur 11.2.3

Additional context

Relevant logs:

Start by reproducing the thread-navigation flow in Google Chrome on macOS: type a reply, switch to another chat, and return to the thread. Compare the composer controls before and after navigation, including the send icon, attachment or voicemail icons, and Follow button. Done means the saved reply still shows the send icon after returning.