Problems uploading files

This is a follow up from the I created a bug report but could not upload a 80Kb tar.xz log file. First I thought it might be a problem with the file size limit. So I tried about 10 free file sharing sites in different browsers, all resulted in an error message. So I suspected it is my computer. I turned off the firewall and tried again - still no success and the same error message. Finally I went to a different computer and there it worked without problems. Now I am at a loss to find out what can cause this problem. Any ideas anyone?

I’m sure I don’t know.

As far as I know, uploading a file is just done the same way as most browser activity. So the firewall should not be involved.

Perhaps check whether some browser extension is blocking it.

I even tried one browser (chromium) without any extension in a sandbox (firejail). By the way the two computers are in the same network - so it is not the ISP or router.

I’m out of guesses.