Description

We've activated RTC with Lab 3.6.1 again for one of my courses. So far all tests had gone well, including one where I had ~ 50 students join a session simultaneously.

But today we experienced again notebook damage, I've put a copy of the damaged notebook here in case anyone wants to take a look. Not sure how much that will help.

Reproduce

We don't know how to reproduce the problem, I'll describe the scenario where it occurred (Facu, please correct any inaccuracies I may report)

1. At 9am, @facusapienza21 logged into a hosted JupyterHub that runs Lab 3.6.1 with collaboration on to teach a class, using his personal laptop. He opened a notebook, used it, and then moved on to other notebooks and activities.
2. Around noon, he went to his office, and logged into the same server from his desktop computer. When he visited the same notebook as before, it had duplicate cells.

In case it's useful, we also noticed two minor strange problems, but they may be unrelated. Mentioning them in case they ring any bells.

1. Facu saw some cells where he'd edit the Markdown but when rendering them, his edits would not show up on the rendered version. Yet they were correctly written to the file.
2. I logged into his server (admins can log in to one another's servers) and opened a terminal to do some debugging. His "running" left-panel tab did not show this new terminal, despite refreshing it several times and waiting. Only after doing a full browser tab refresh, did he see the terminal I'd opened. At that point, he was able to access it fine.

Expected behavior

User notebooks are not corrupted by JupyterLab :)

Context

• Operating System and version: Clients are MacOS, server is JupyterHub with Ubuntu 18.04, full config here.
• Browser and version: Facu?
• JupyterLab version: 3.6.1