The machine wants to know that it is oriented and in position for ATC to take place so I would guess one of those sensors is on the borderline. Have you checked that the in position lamps are on when it hangs up? Try adding an M19 on the line before the toolchange and see if it will hang up there. Maybe it’s “confused” and a T0 before the last tool or an M33 to clear all tools may change its behavior.