Here is the log file with the 404 near the end: https://pastebin.com/zxgzNYqd
And when this happens, the "temp" folder in the Factorio Appdata folder becomes corrupted and needs to be deleted with filetable editors. Namely it stops being visible in Explorer or via command prompt, but conflicts with attempts to create a new folder with that name.
Current update 404s on downloading, corrupts temp folder
Re: Current update 404s on downloading, corrupts temp folder
Hello, Factorio wasn't able to remove the temp folder upon start? Can you provide a log file of how it fails if it happens so?
Re: Current update 404s on downloading, corrupts temp folder
Does the attached log not contain that?
Also, this issue has resolved itself - probably because the 404 no longer happens - making it impossible to get another log. However, I suspect the underlying problem of "filesystem error if the update errors" remains present.