Looks like that event is just Steam deleting a temporary file that was used for the download, after copying the exe into its final location in SteamApps/common/Fleshcult/fleshcult.exe. If there's no deletion from that final location, that suggests that Steam couldn't write the file there in the first place.
To get a broader picture we could try removing the filter for deletions and replacing it with
Path Contains fleshcult.exe then Include
Install fleshcult yet again and wait for it to get deleted again, and you'll get pages and pages of events. You could save the log as a spreadsheet and send them to me. To do that, go to File -> Save... and pick Events Displayed Using Current Filter and Comma-Separated Values and hit OK. If you could email it to me at jack@fleshcult.com I'll pore over it and compare it to what happens on my computer.
Dang, it's really crazy that this is necessary. I feel gaslit and I'm not even the one that it's happening to!