End crystals are knocking people upwards even when the crystals are above their feet (which won't do much damage if you have the correct gear just like in the video below). It's as if these players are taking the same type of knockback as when a player hits them.

How to reproduce:

• Put on some netherite armor.
• Give yourself resistance level 255 or do anything else to stop yourself from dying like eating golden apples.
• Get yourself in survival mode.
• Place an obsidian in the same level as your feet, and spam place and break end crystals on that obsidian.

The bugged knockback will be a lot more severe if netherite armor is not worn due to the knockback resistance the armor gives.

Here's a video as a demonstration:
https://www.youtube.com/watch?v=6TdEQN0EuB0