I found parrots actually do dismount. You just have to be running and jumping so they don't immediately remount, so I guess this isn't actually a bug.
I couldn't figure out how the one attached world is supposed to work and I don't have the worlds with screenshots or videos, but the problem happens in this world.
[media]Marco and Kai,
This is a bug report for the Bedrock edition of Minecraft. If this is an issue in Java edition, you should check for a bug report under the Java edition project.
The bug report for this issue in Java edition can be found at MC-186067
I have the same issue on Android.
My problem was too many chickens. Mobs are spawning now.
I have the same problem on a Moto Z3 running Android 9.
This is a problem in the 1.16.0.60 beta release on Android.
I also have this issue. It doesn't have to be just one item that you double tap on. If you double tap on any stack of items to merge the stacks, it doesn't work.
I just did that and it worked so this isn't actually an issue.