OK. The first mission is definitely affected by this bug... not to be confused with the training missions. I tried it under the latest knightly (2023/04/05), and the 23 release build. It has no debriefing under either build. I'm also concerned about using earlier builds, as I got a ton of error messages during mission load as soon as I switched back to 23.
Update (rather than another post):
Got no debriefing for M14, either under the newest Knightly, (04/07) or 23. I thought it might be due to the new fade-to-black ending rather than the old land-at-carrier from the old ones. One possibility, is that, since the mission uses a send-message-list instance associated with the completion event tied to the debriefing stage, and since I'm using TTS, and since it fails to read all of the messages out before fading to black (a bit of a nuisance for me), perhaps its not reading the event as complete. I'll tie it to the fade-to-black event that follows and see it if makes any difference.
Nope. That didn't make any difference. Weird.