A number of people have said they had the error in the TBG mission "Lightning From Heaven" where when the Gabriel comes in it doesn't fire and just sits there (I've encountered this error on 21.0, 21.4, and 22.0 but the mission works okay on 19.0).
Herkie is working on an update to fix this that should be released in the relatively near future (though I don't have an exact time frame).
In the meantime, I thought of a possible solution that might work (on the other hand it might not...I haven't fully tried it yet). What is supposed to happen in the mission is that the Gabriel destroys three of the enemy destroyers and then the enemy flagship surrenders.
If you're having this error with the Gabriel (and aren't able to use FSO 19.0), could you try using cheats to destroy the three destroyers (other than the one marked as Akhmim's ship) and see if that triggers the surrender dialogue which should end the mission?