It is possible the repair guy did something shady, but hard to say for sure.
The vibrator is part of sdcard tray and that connects direct to the logic board, the other sensors would be effected by the main flex cable so there really isn't one cable that would cause your issue
The mac address and imei are located in the efs partitions but I'm not 100% on the serial numbers location. Yes it is possible to change this using JTAG but I don't think it would be necessary nor do I think he would bother to
Unless all he did was swap logic boards and to make all look legit he matched the imei, not sure of a reason to do all this though
I assumed everything worked prior just fine? Does the phone look the same? (Same scratches etc?) Is there a void sticker on one of the three screws in back? You willing to open up your phone and look around to see if anything is suspicious? (There should be tape in certain places that can often give signs of tampering
As for a fix, it all depends on the cause, which is hard to determine as of now
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