When the mod was on fabric, splashes appeared exactly where entities landed:

Now, on quilt, the splashes are locked to the block grid:

Note to devs: It seems like the problem is not with the water splash function itself, but rather the input values.

Update: I got a feeling that it has to do with quilts entity.getX() and entity.getY() outputs. They are supposed to be doubles, but it's the only reasonable cause to me at the moment.

Fixed in latest