Even though mobs aren’t supposed to spawn in a Deep Dark city besides the Warden, there are a couple mobs who can. Firstly, I do believe it needs testing to confirm but I think Illager Captains can spawn under the surface, specifically in Deep Dark biome (Which could cause annoying vibrations and disturb the Warden.) Endermen can teleport inside the city (It’s more of an issue than you think), and they don’t run from the Warden, so that could mess gameplay up. The third mob is the Wandering Trader (Yes I searched the issue) and it might not be an issue if the Trader spawns in the City, but if a Raid Captain and a Wandering Trader spawned in at the same time, the Trader would die, a Sculk Catalyst could form Sculk, and then more vibrations could travel and activate the Warden “accidentally”, thus ruining gameplay.
Linked issues
Attachments
Comments 1

Thank you for your report!
We're tracking this issue in MCPE-153524, so this ticket is being resolved and linked as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.
Quick Links:
📓 Bug Tracker Guidelines – 💬 Community Support – 📧 Mojang Support
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki
-- I am a bot. This action was performed automatically! The ticket was resolved by one of our moderators, and I left this message to give more information to you.