I wonder how knowledgable your shop guy is. To check for a bent idler wheel all that is needed is to press the bow to remove string pressure from it and spin it. OK, the string was pff the wheel and the bow was in a press. Why didn't he just spin it and see if it's bent.
Check the idler wheel for excessive "cam-lean" and correct it if it's leaning badly.
I have to ask, though. Were you drawing the bow by hand, meaning with your fingers? When you tried to let down had you drawn the bow with fingers? If so it's quite possible that you torqued the string right off the idler wheel much the same as a bicycle chain comes off a sprocket. I've seen this happen lots of times with short axle to axle bows being drawn or let down with fingers.
Or are you gripping the bow when drawing or letting down? In either case torque can twist the bow sideways and the string can pop off.
I will commend you for not ruining a second set of strings before finding the root cause of the problem.
If You're Not Living on the Edge You're Taking Up Too Much Space
Martin/Rytera Staff Shooter
PSAA Life member, UBP Life member
PADI AOW Diver