I sent my M1 to Orion7 in New York, Athony Pucci is recommended in the books Ive read as an excellent M1 guy. I had her redone, new barrel intalled I was told she in now shooting tight groups at 200 yards. I paid for two day shipping from UPS and they lost her!
If it were stolen by an employee, it must have only been a driver. UPS hub's have a lot of security. Employees can't even take their phones into the hub's. They go through metal detectors on the way out.
While it is not impossible that it was stolen, I would say more likely to be lost. if it got put on the wrong truck, it could be shipped across the country before it was found out. Could be a while to get it straightened out.