There is a prison guard at Broad Arch, but no door.
I'm not the developer nor the tester but am verifying this MOD and reporting bugs to the Bug V8.* board in order to expect improving. After I realized your post, I visited all castles and towns to check prison doors (and some other doors).
The report I've just posted. For your information:
"Prison doors (The player met himself again)" (https://www.aworldoficeandfire.co.uk/forum/v8-0/prison-doors-the-player-met-himself-again/)