I have had

Crowns repaired in a laboratory are usually as good as new so long as they have not been worn in the mouth for a protracted period

Usually these are repaired and refired with no problem , it is adjustment itself and high crowns that break crowns , look at occlusion .

TJ is the expert
Adjusting crowns creates microcracks (like chips in a car windscreen) which can propagate over time leading to fractures and chipping
Certain types of ceramic are more prone to this such as Zirconia which although tougher can show chipping over time which is difficult to repair in the mouth as one cannot use the extreme temperatures of the oven used to fire the ceramic

Implant crowns should be of higher precision than regular and especially HS crowns! However minor adjustments are often necessary. It allows the dentist to be in control of the strength of the contacts between the crown and the adjacent teeth as well as the contact with the opposite tooth. I am glad that the crown was send back and not fitted. Sometimes it is necessary to send back the work to the lab. This doesn't have to mean that either the lab or the dentist is bad. It should reflect that your dentist was unhappy to fit the crown and therefore sent to back to have it improved.