Losing changes to sounds after power off

Hi

I’ve been having a problem with my (second hand & out of warranty) Digitone.
Right after getting it, I noticed a problem.
After cycling power, changes I’ve made to the pattern and to sounds within the pattern are sometimes lost.
This is with an empty project, not in slot 1, and not locked.
Has anyone had experience with this?
I’ve contacted Elektron support but after initially being responsive I’ve not heard anything for a month.
Test mode does not show any problems.