The trial began, and the main lawyer we invited was not present, only his assistant was called. What kind of situation is this? Is it common?

It can't be said that it is very common, but sometimes there are cases, not to mention violations, because legally speaking, the parties entrust a law firm, and the law firm can decide which lawyer to assign to appear in court, but generally it will assign lawyers according to the designation of the parties, and lawyers who are not assigned under special circumstances should appear in court.