They used to fall as miniature ice blocks but now they are big ice blocks that glitch a lot and the sand layers from sand storms are a lot (too much) and replace water...Replacing water causes it to look glitchy.

This issue is halfway fixed, here's the screenshot of falling hail in weather2 2.6.4 and later:

NOTE:I need to disable particle precipitation to make the hail visable.

I wonder why they are falling as big ice blocks, on 2.2, hail would fall as big ice blocks, so coros decided to bring big ice blocks back.

Oh nice yeah thanks for the hail bug, I recoded the block renderer and messed that up looks like.