We recently updated from 1.14.4 to 1.16.1. Everything went fine. But now I discoverd an issue belonging to Mushroom Islands. Not only did the shore change, some blockbioms changed from mushroom_island_shore to ocean or cold_ocean and visaversa (we could live with that), we also now have regular mobs (like skeleton, zombie, creeper, spiders, enderman) spawning on the shores.
What we did before the update was enlarging the mushroom island as far as possible as long we got mushroom_island_shore to benefit from the complete island.
I checked all of the blocks at the shore and removed every single ocean or cold_ocean block, but mobs are still spawning. We also have the effect on other mushroom islands at our server.
Added some screenshots with mobs, where we never had mobs before.

I'm pretty sure its a bug, but not completly sure if it happens on other servers too, or we are the only ones.