Check the 2 locking nut screws behind the neck. Those will come loose, and cause it to go out of tune.
If it's a bolt on neck, check the 4 neck bolts. They gotta be super tight.
Ya might as well check the screws that hold down each string saddle too.
Often it's the locking nut. Sometimes the strings are not clamped enough too. pluck each string, while it's ringing, push on the string behind the nut. if it goes sharp it's not locked down properly. Also, the posts have tiny locking screws inside the post. those should be tightened down.