This bug is probably related to MC-260599.

How to Reproduce:

Step 1. Place a repeating command block in a spot that is completely exposed to the sky (only air blocks exist above it).
Step 2. Loop the following command in that command block.

execute positioned over motion_blocking run particle minecraft:bubble ~ ~ ~ 0.1 0.05 0.1 1 100 force @a

Step 3. Place any kind of banner above the command block (preferably a couple of blocks above).

What is Expected:

Notice how the bubble particles appear the block above the banner's hitbox. This is incorrect. The particles should appear at the block above the command block as banners do not block motion.