Not sure if this helps to narrow things: I am facing a similar behavior (maybe exactly the same) as mentioned here Something wrong with web UI - #3 by kenkendk
Fun fact is that also my remote backups are on Storj. However, they have been working fine for more than one year with daily backup operations.
I am still in favor of thinking that Duplicati upgrade might be the root cause (since we are sharing the timing at which this issue popped up) but it might also be related on some changes that Storj could have been done, even though I am not aware of anything.