On a ship with a low-speed diesel when the ship was heavy, going from slow ahead to half ahead the engine would get stuck in critical speed range and the alarm would go off. The cure was to give a full ahead bell till the engine pulled out the critical range and then drop back to half ahead.
Ahead bells only, Ok astern and didn’t happen when the ship was lightly loaded.
I discussed this with the chief a few times and he insisted it was just because the ship didn’t have enough power, which didn’t make sense. A few years later, after I got off I ran into the chief and he told me they replaced/adjusted the throttle linkage on the main engine and it solved the problem.
Later I ran into a similar thing on two different ships. Any comments or experience with this elsewhere?