This is my guess, but I’d have to hand you a debug version.
Pi is a 32-bit ARM architecture. The calculation we use might be overloading the value on the Pi. So, if you can live with a few less days of backups, I think that will get ya going. I will debug on my Pi 3+ in the next week or so.
What was happening (I think) is the value calculated for millseconds in a month was “rolling-over” and telling the job to delete the file as soon as it was created. If this is the case, I’ll see about changing the math over to not comparing to the milliseconds on the system to seconds or minutes up front and using smaller numbers for compare points.
Sorry for the troubles, and thanks for sharing the config, that helped me out a ton in taking a [reasonable?] guess.