Room members list infinite scroll loader does not get all users

Description:

Scrolling to load users in a room does not work. We tested with 105 users, of whom 1 was active, and only 103 showed up.

Steps to reproduce:

1. Open room members sidebar.
2. Use All members search.
3. Scroll until end. Sometimes it will stop and you have to scroll up first. Sometimes you reach near the end and it never loads more. (103/105 for us.)

Expected behavior:

Loads all users. If already at bottom of list upon render, preemptively load more.

Actual behavior:

Fails to consistently load all users.

Server Setup Information:

• Version of Rocket.Chat Server: 3.11.0-develop
• Operating System: ContainerOS
• Deployment Method: Docker
• Number of Running Instances: Scaling
• DB Replicaset Oplog: -
• NodeJS Version: 14
• MongoDB Version: Atlas

Client Setup Information

• Desktop App or Browser Version: Safari and Chrome (only ones we tested)
• Operating System: Mac (Windows untested)

Additional context

Relevant logs:

Reproduce the issue from the room members sidebar using All members search and a room with more than 105 users, testing the scrolling behavior in Safari or Chrome. Trace the room members list and its infinite-scroll loading entry point; done means every user loads reliably, including when the list is already at the bottom on render.