ENGINE-16004 error on Task Complete REST action

We’re encountering an issue with closing a task via the REST API – we are getting error “ENGINE-16004 Exception while closing command context: null”, and other references to this error seem to indicate it would be related to the Process Instance being cancelled, while the PI is definitely still alive here. This workflow has been working fine for some time, so we’re at a loss to understand what caused this to suddenly go awry.

Any thoughts how this might have happened – and, particularly, how we can resolve? (I’ve tried many different things via REST and Cockpit, but have not been able to get this Task completed)

Thanks!