Reproduction of this issue:

• Composter
• then put block 2 blocks up the composter
• put water above the block
• surround the water with any block so that it wont leak
• put villager inside composter
• and watch it getting sucked up into the water through the block.

I tried this with wooden block. Idk about other blocks. Glass block also works

-I haven't had time to get a video or screenshot of reproduction for this bug but I might add it later -here's some illustration:

[water] <-- surround this with wooden block
[wooden planks]
[empty]
[composter] <- put villager here

Edit:
I notice this issue when I was trying out my existing world in 1.16 pre-release 4. Then an hour later, pre-release 5 was out and tried it again and this bug still existed. Haven't tried it on 1.15.2
I attached some pictures that demonstrate the bug. As shown, glass and planks works with this bug. Haven't this with every other block. I blocked off the top to show the villager and prevent it from escaping.

Cauldrons also make this bug works. Instead of putting the villager inside a composter, you put them in a cauldron and they will still get sucked up.
I have a hunch that this might work with players as well. Well test it later. Does not work on players.

Zombies: Doesn't work also they float then they clip out of the block then getting out.

If I'm not too lazy to check every 2 block entity for this. I might continue updating this what works and what might not work.
For now I already tested 2 types of entity that is 2 blocks in height:
[RED - works]
[LIGHT BLUE - does not work]

• Villager
• Zombie
• Any entity that is 1 and 3 blocks up in height.