User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Firefox/91.0

Steps to reproduce:

1. Interact with the folder contents pane (possibly limited to deleting/archiving messages)
2. Get lucky

Actual results:

For as long as I can remember, this has intermittently resulted in the folder contents pane going blank until I switch away from the folder and back to it to get them back.

Since I had no idea how to give more information, I've just been sitting on this hugely irritating disruption to my workflow (and part of the inspiration for an on-hold project to write my own mail client with a novel UI design that began as my final project for my bachelor's degree) for a decade or more but, recently, I discovered a few things about it which inspired me to report it:

1. I forget what I did, specifically but, in the last version I was running before 9x.x, if the resulting blank folder pane was spun off into a new tab, it became the welcome page. (Suggesting that whatever internal URI is being used is getting set to an empty or null value.)

2. I noticed that, when it happens, all but one or two of the toolbar buttons in the message pane's header vanish. (eg. When it happens, I lose the ability to delete/archive the currently visible message until I switch away and back)

3. Once, waiting 10-15 seconds caused the folder contents to come back on their own. (I've only ever waited that long once, just before typing this up, so I don't know if it happens reliably)

4. It's possible it's not purely random but some kind of race-condition between deleting/archiving a message and some background operation.

I'm now running the Flatpak release of Thunderbird, so, aside from the difficulty of triggering the problem on command, it should be fairly easy for me to give updates on whether the bug remains in future versions.

Expected results:

Interacting with the folder contents pane should never cause it to spontaneously go blank.

Aha! Hypothesis: The folder goes blank if Thunderbird decides to compact the folder in response to a change and, if it's a large folder (possibly with a lot of unread messages, possibly an RSS folder), then the process takes more than a split second, but the "going blank" aspect can be overruled by switching away and then back.

(I just saw it happen with my Phoronix RSS feed folder, which had been allowed to build up 3963 messages, 3772 unread. I didn't flip away and back because of my previous experience with it coming back on its own if I wait, and I noticed that it seems correlated with a status bar progress bar and a "Compacting ..." message. I also noticed that, for that folder, it took somewhere around half a minute.)

I figured out how to get it to go to that welcome page. Switch to another tab and then back while the compacting process is in progress.

I believe I am seeing this or a similar bug also, where after deleting a message the list of message goes blank. Unlike the original reporter though, this is something that I have only started seeing happening in the past few months. I am running Thunderbird 91.4.1 32-bit on Windows 10.

I have rarely seen the message list come back on its own, but normally have to switch to a different folder and back to get the list to reappear.

I have not noticed this being related to compacting but have not been looking for that so it is possible it is and I haven't noticed.

Safe duplicate.

I'm not sure it IS a duplicate. That bug says a restart is required to get it back while, in my case, just switching away from and back to the folder does the trick.