I also added a MP4 file showing mobs spawning.
You closed it but here it is in 1.16 pre-release 5 vanilla i added more screenshots. same biome same issue.
I translated it to english does it work that way or do I've to recreate a ticket?
Thanks for letting me know that tickets has to be written in english.
confirmed in 1.16-pre5 added a mp4 files showing mobs spawning in those grass_blocks
and a screenshot showing the grass_blocks within Minecraft:ocean biome instead of mushroom_field_shore.
seed : 1869945237501097058
coordinates : -2717 81 -3462