Yup, originally when I had this problem I was suspecting bad RAM, but I was having different issues just the other day: How to recover from "snapshot does not exist"?
TL;DR Jottacloud are not completely reliable. My backup script every now and then fails with rclone/jottacloud errors, and usually recovers after few days without me changing anything. The problem I just had also seemed to be related to jottacloud, not really bad RAM. The good thing I guess is that they seem to always eventually work, but of course this does make me worry if they are gonna fail eventually corrupting the repo.
They are really cheap if you store a lot of data, but not the greatest. I’ll probably keep using them as a daily/weekly backup (they don’t charge for data transfer) but I’ll duplicated the same repo somewhere else doing ~monthly copies, just to be safe.