The reason why drowned aren’t spawning in the dripstone caves is due to an error in the spawn code, for dripstone caves, the drowned are set to “spawns_on_surface” instead of “spawns_underground”, which means they will only spawn in dripstone cave aquifers exposed to the surface. Changing the “on_surface” to “underground” fixes this and allows them to spawn, but preferably, simply add “spawns_underground” below spawns on surface allows them to spawn in all dripstone cave aquifers regardless of if there is air exposure or not
Linked issues
Attachments
Comments

Thank you for your report!
We're tracking this issue in MCPE-144066, 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