i've seen the same issue since around May, same issue in multiple browsers, i've rebuilt the container since then too and still have the issue so it doesnt seem like a config problem.
I'm assuming most other people add files differently, I've resorted to using a monitored folder but its a pain when i want ignore some parts of the download.
Sadly im seeing this too since the last release, I've switched to using a monitored folder and have been adding the torrents there and they get picked up all at once.
I didnt see anything in the logs but the browser console throws an error "TypeError: Cannot read properties of undefined (reading 'filename')"