Floor disappears

An 18 by 32 rectangle of floor has gone missing on our world three times and it's purely random, we exploded some floor and nothing was wrong so we had a check around in case we missed a spot and on our way back we saw a huge rectangle of bedrock was unloaded, I jumped in and I fell out the world, I realized it had disappeared, we're scared it could happen to one of our builds

Sincerely

Steelybeatle265

P.S we filled the holes in but they're roughly this big except the inside is missing as well