The bug

Since the new parity changes are coming to Java Edition, there are 5 new gamerules from bedrock edition, one of them being fallDamage.

Theres a bug with it at the moment when updating other worlds to the latest snapshot. It seems that fallDamage automatically sets to be "false".

Here are 2 different clips of differences before the parity came to Java (19w35a) and after when they were implemented to Java (19w36a)

I didn't use the command since I made a test world before 19w36a to show that this glitch exists.

NOTE: When creating a new world with the latest snapshot (19w36a), fall damage will happen as nothing happened. It only occurs when updating other worlds!