In a couple of decades running Linux installations of all flavours, I have never seen anything in lost+found!
fsck on large hard drives was scary on how long it could take to finish.
(At least this is what my memory is telling me. I could be mistaken, but that's what I remember.)
I recall going to sleep and it still not being done when I woke up. Bleh.
When you have dirty writes in the kernel that have not yet been written to disk, in the old days of ext2 (before XFS was ported to Linux) if the power would go out, or you would have a bad disk, when fsck.ext2 would run, if files could not be matched to a directory, they would placed in the /lost+found as, and hopefully my memory is intact, as inode numbers, so you would have 1232342343, 123246564 etc and then you would have to look at each file to figure out what it was and where to move it if it was salvageable.
Brought back some memories.
But I think ext4 will only let things appear there if you change some default flags.
At one point, I had one where the directory structure was completely broken and had circles in it (broken SSD). To be fair, in that particular case, I did not look for lost+found and just wrote a tool to extract the data manually that I was looking for.
I saw it often. Running fsck on a crashed/failed partition usually does put some files in there. Maybe I kept using old hardware too long...