Ahh, yeah I just tried a patrol with a XXI.. it was.. deadly.

Jan 45, right through the English Channel! Was going ok till south of Dover when I hit a mine. For somereason, even with a mostly rested crew my engines wouldn't work. Granted I was at a 15% battery, but still.
Finally ended up coming to rest ON another mine, kissed it a few times actually, but stopped right under it. Couldn't do much.
Got 5 destroyers on me, depth bombing, but I was on the bottom 37m and they weren't really hitting me.
I was able to reload a last torpedo and blind fire it.. SUNK A TRIBAL!! One shot.. blind.. 37m down! I RULE!
Finally grew bored and dumped all my air into surfacing. Made a run for it on diesels.. that went.. badly.
So yeah, there does appear to be a lot of little issues with the XXI.