It appears that upgrading my bridge to v2.10.21 firmware has cause IncreaseSpeed and DecreseSpeed actions on my fan to stop working. I still get a 204 status code returned, but the speed does not change, either in the app or physically on the fan. SetSpeed is still working. My integration attempts to increase/decrease the speed by 1.
I am not 100% sure it was v2.10.21 where it stopped working, but I can verify that it was definitely working on January 16 (last time I tested and pushed a version of my integration).