I know, this is probably a duplicate of something else, but I couldn't find anything for this version.
When new chunks get generated, blocks, that are supposed to fall, don't fall until they get a block update. This creates the floating gravel in the Nether, floating sand in the overworld, etc. Easy solution: Let every generated block get a block update as soon as it gets generated. Yes, a bit more lag, but also a big bug less. It would also help and create less lag if random ticks create block updates. But then people who use bugs (BUD) complain if that gets fixed.