Repair

If you sent it in to Apple for repair and they found no issues, did your issue occur some or all of the time?

If it occurred all of the time and the issue you sent it in for is still there, I would contact Apple Support again and resend it in. If they refuse, I would suggest that you speak to a more senior employee.

If it only occurs some of the time, I would suggest that you inform them of that, and then attempt to send it in for repair again.

Take it back to whomever repaired it and make them make it good.