It happened at random. At some point auto-save just started endlessly looping, and after plenty of minutes I had to terminate it. The document then was destroyed. For the record its size was 360MB.
It could be that the bug has been there for plenty of time, as there are many potential duplicates:
Endless autosave loop
Loop in autosave
autosave locks program into continuous loop
If you need the document email me for it, as this bug-tracker hangs while uploading it.
Arch Linux, libreoffice-fresh 6.3.4-1
I've also experienced this issue twice in the past 2 weeks with an ~825K .ods file. (The first version of this file was created in Sep 2018 and I did not experience this issue until Jan 23, 2020.)
I believe I've identified the culprit on my system. 2 weeks ago, I re-enabled a thumbnail maintenance cron job which runs weekly. What I didn't realize is that /tmp was filling with 0-byte magick-*.pam files and magick-* symlinks as a result of this script.
When I deleted these 0-byte files, Calc completed an autosave and stopped looping.
I didn't think to get a count of the 0-byte files, but I strongly suspect the issue is a lack of available inodes in /tmp, since LO also uses /tmp while creating the auto-save.
I'm not sure it's within the scope of LO, but perhaps the autosave code should exit and warn the user if LO is unable to create the necessary files in /tmp?
Alberto, please write your OS. Is Kevin's case related to yours?
It could be the same issue, as I'm using Manjaro Linux.
My drive died three months later...