Whenever we close a support ticket at my company, we note the resolution to the problem so that future technicians can see what we did to solve the issue. We also send the resolution to the customer so that they can see what we did to fix the problem.
On occasion, the problem will be fixed but we do not know why. We usually put "the problem has been resolved", but this doesn't really give any information to someone looking at the ticket in the future.
I'm looking for a word or phrase that means essentially, "The problem fixed itself", "We don't know how this was fixed", or "We don't have a resolution, but it works".
The issue with these phrases is that if a customer reads them, they might feel like we're incompetent, or that the issue isn't fixed.