Well, on the assumption that the engine didn't do this pre-shop visit, one would tend to be suspicious of the changes made during the shop visit. Maybe there's a rotor with excessive tip clearance (God knows how) and it's screwing things up in the HP compressor.
Incidentally, is the surge being"fixed" by opening bleeds in the LP or HP; that might tend to point the blame at part of the engine.
Other than that, was anything else changed? Fuel control system? Though if they've had the engine on and off the a/c a couple of times its hard to believe a common mistake was made in stallation .... if the same team did it each time ....