Sometimes the Tinyhawk 2 gets messed up and the VTX goes back into locked mode. If you recently upgraded the FC to betaflight 4.2.x this may happen. The result is that it gets stuck in 25mW on A band. To make sure it's unlocked, boot it up while holding the button on the VTX. It's located right above and behind the USB port on the VTX board.
Also if you are using Betaflight 4.2.x you need to make sure your VTX tables are correct. As you probably already know, you can set the active channel and Power output in Betaflight.