I had similar issues with 18.104.22.168. To me it seems that the parameter assynchronous-upload-limit is not considered any more - and so Duplicati creates more and more files until the whole system is unoperational.
I don’t believe Duplicati will retroactively clean up local temp files from previous runs. The easiest method is probably just to make sure Duplicati isn’t running any tasks and manually delete all dup-* files from your temp folder.
Please let us know if being on 22.214.171.124 has “resolved” the issue (at least in the sense that you’re not still getting more temp files).
Of course retro-active cleanup isn’t such a bad idea… maybe something that just says “delete any dup-* files from temp that are older than the last STARTED backup time”.