After the update, the blocks that were added via add-ons have disappeared and they were replaced by air. If trying to add and add-on which includes any blocks, the blocks will not be able to be obtained in any manner, as if searching in the creative menu or writing a command. That means that now, these add-ons are useless and they will be, unless the bug is fixed. However, the textures of in-game existing blocks still can be changed.
Steps to reproduce:
1) Download an add-on which includes any new blocks that are not in-game.
2) Apply the add-on on any world.
3) Try to look for the blocks featured in the add-on.
Expected result: blocks from the add-on will be able to be obtained via creative menu and commands.
Observed result: blocks cannot be obtained neither via creative menu nor the commands.