Type: Server
Operating System: Linux (Debian 10)
Server Version: 0.3.7-R3
Plugins Installed: Yes
Plugins (If above is yes): [font=Monaco, Consolas, Courier, monospace]streamer, sscanf, mysql, filemanager, pawnraknet[/font]
YSI Included: Yes (y_iterate, y_hooks)
Output (Logs): [font=Monaco, Consolas, Courier, monospace]https://pastebin.com/j4NhpLBC[/font]

[font=Monaco, Consolas, Courier, monospace]This crash happened suddenly and it was only once, it had never happened before in this way, what could have caused it? Considering the log, it doesn't seem to be related to any plugin...[/font]

Post related to your problem: https://github.com/Zeex/samp-plugin-crashdetect/issues/32

If you do not have the latest version of crashdetect, update it.
https://github.com/Zeex/samp-plugin-crashdetect/releases

That does not seem like the same trace, thus probably not the same bug. However, fixes.inc covers the mentioned valstr bug (plus many many more) so it might be worth adding it to your script and seeing if that helps. Of course, if this has only happened once and you don't know what caused it it is very difficult to help you fix it. We need a reliable way to reproduce the bug to start narrowing down the cause.

I tested with massive player connections / disconnections at localhost with bots, the server always crashed after a while.

I removed the include y_iterate and it didn't crash anymore, so I think that was the problem. My YSI version is 4.00.0001.

EDIT: y_iterate was not the problem, I still don't know what can be...
EDIT 2: I upgraded YSI to 4.0.2, it seems to have solved it, I will do more tests.

That version of YSI is years old. Get 5.x

Thanks, upgrade to YSI 5.x stopped the crashes.