Terrain takes long to load, player hanging in mid air

This probably happens only with bigger maps (more explored). I played this world for three weeks.

After selecting a world to play, it goes through the "preparing spawn area", "progress.working" etc messages, then starts the renderer, but the world does not load until up to about a minute later. Meanwhile music plays, once I got murdered by a illager party, but it doesn't display. F3+A doesn't do anything, changing render distance neither. Sometimes reloading the world helps, other times I just wait until it finishes its slow loading.

this never happened to me before the last few snapshots.

(i'm almost certain this will be marked as a duplicate, but searching for "slow load" is fruitless, there's just too many different issues about it)