Buildings and mines re-exist on some places

The world randomly changed, i made a "cave/path" thing underground (tunnel in Dutch) but everything randomly disapeard, so i got in spectator and i saw a piece of my cave thing got filled up again. next to that a line-mine randomly moved to 100 (or so) blocks further. so a whole piece of my country got randomly filled up while i was in an sea-ocean (also no elders in there?) and a big piece got randomly placed somewhere else. it messed up my redstone works there and i spended like an hour on getting that out but if it randomly refills (with ores and stuff also in there) i dont like it really much anymore. maybe saving problem? but i dont think so...

yeah so here it is

i tried to screenshot it, so i did but i only got a load thing, even tho i was in game, very weird.