'Was(Is?) the problem resolved? (- passive voice)' is correct, I think.
('Did you resolve the problem?' - active voice)
Well...if 'resolve' can be used as an intransitive verb, "Did the problem resolve?' could be possible...but I haven't been able to find any examples of it so far.
<transitive / intransitive>
I walk in the park. - intransitive
I walk my dog in the park. - transitive
I'm not a native speaker of English, as you know.
Please wait for the native speakers to respond.
Student or Learner