@mdw, you are welcome. And, Who said it was going to be easy? 
Seriously now, you don’t need to provide the developers with a failing instance. If you yourself can access it now, it would suffice for you to preserve it in that state, and then open the issue and follow the developer’s instructions – they will most probably be able to pass you binaries and commands to run to try and track down the problem.
Tracking down and fixing it would contribute to make restic more robust and an even better piece of software than it already is, which would benefit everyone.