Getting hot is 'normal' (you are locking it in position by energizing the coils). is it (much) hotter than the other motor?
If you grab the output shaft and twist, does it move/rock, if so, is the other motor just the same? (could just be low torque, so comparative force to move the shaft)
If the motors DO behave differently (but the same motor type), is it possible to reverse the motor electrical drives - you may need to disconnect the motor output to prevent damage.
If the problem moves, you have an electrical/drive/software problem.
If not, then you have a mechanical problem. Disassembly of big motors is quite easy, you may find that the field windings have broken loose and are able to rotate, although that may be accompanied by a lot of noise while in motion. It may also be a single coil that is defective. This may not be noticed if positioning is via some form of encoder rather than absolute stepping, only when holding would a problem manifest itself.