How to fix my friends mob farm? (Bedrock)

So my friend is playing Minecraft on Bedrock, he wanted to make a mob farm, but then the mob farm stopped working once he added a dungeon spawner to the farm.
How can he fix it and continue getting XP from is farm
Things we tried:
- Disabling the spawner
- Lighting up the caves around
Here is a video for if you need it:>!https://youtu.be/C2YvAJsSzEs !<