Crashing only in town, most likely someones mtx

Crashed in town like 50+ times for real since league start
if anything pops up its small window with https://imgur.com/a/ezoJKkY

Yeah, I have had this several times now, always in town.

I have had the same problem. The game only crashes when I join an instance that another player is in or they join one I'm in. It's somewhat infrequent, as it doesn't happen with the majority players, so it's probably related to a mtx like OP suggested. I should also note that despite the game crashing, I'm still in the party, so when I get back on I often can enter the person's instance or they can join mine, which so far hasn't resulted in another crash, for some reason.

Another possibility is that it's related to Vulkan. I recently (a week after league start) got a better gpu and switched from DX11 to Vulkan. I never got this problem before the change. I'm going to try DX12 to see if this error pops up there.
I'll edit this post if anything happens.

Here's two screenshots of the error message:
This one always pops up
https://imgur.com/6h6gLFi
And when I press "ok" I get this one
https://imgur.com/tc6DNUJ
After pressing "ok" on this the game completely closes out.
While these two messages are open the game is completely frozen.

I took this screenshot of the bug report reference number, but it probably doesn't help since I used the /bug command after the crash happened.
https://imgur.com/pcJvp1X

Yes, this is a Vulkan-specific error message (vk). I started getting the message last year and found switching to DX fixed the issue for me.

Same as you, I got a new PC last month, tried to switch to Vulkan, saw the error message again. Switched back to DX, no errors.

I unfortunately have not found any good ways to fix it so I can play on Vulkan yet, but as long as I'm not crashing.. I'm happy to keep playing on DX.