A double tap is when two circuits ( wires ) are hooked up to one breaker. Most breaker terminals are designed to take one circuit or wire.
A double tap is a safety hazard.
Overheating of the circuit is possible and if one of the wires is not properly fastened there could be arcing . Nuisance tripping has also been reported by clients and is a warning of a problem.
A Home Inspector can check your electrical panel and advise of any problems. I would also suggest that a licensed Electrician be called in to make the repairs.