chunk loading errors reloading 1.15 pre release

Yesterday me and my friend were playing on a LAN world and i had left it for about 15 minutes running both of us afk. I came back to it and I thought it had crashed but i was able to get into the pause screen and close it after a hot minute.

However when i came back to it this afternoon alone i noticed the terrain seemed a bit strange so i went into creative to see a bunch of new chunks loaded on top of the old chunks in a grid. it was originally a stone mountain area. i showed it to one of my other buddies and we're both completely baffled by this. It seems to only affect the area i re-spawned in. the further i traveled out it seemed to be the normal terrain. The initial setting i had was 7 chunks for render distance but i don't think that really has much to do with anything? might affect the amount of area this was but i dont think thats exactly the case. its perfectly playable nonetheless besides all the strange mis-matched chunks in that area.