They can go through behaviour changes when a cage mate is lost!
Peggy, after Dot died, became a vicious bar chewer and she was moved into a ZZ2 to stop this. She was also very hyper and demanding of playtime. But it had the oppostite effect on her tameness as she became much more sociable and loving towards me
I can certainly imagine a syrian smell sending him wild, try to be really careful about thoroughly washing hands inbetween handling and keep the cages far apart if possible