[PvK]

You can also try turning ministers on and off for a few turns at a time. I can't remember off-hand if the unit-building minister is different from the ship-building minister or if they are the same, but if so, then turning off ship-building might get some units in the queue.

Otherwise, I think the AI might prioritize ship building over unit building, and so not build units until it fills ship quotas. And/or it might be related to the current AI mode.

PvK