weird glitch?

So my friend and I have been playing Minecraft on this world for at least a week. We had at least 10 buildings with farms inside. him and I afkd while we talked for a while away from the terriformed island we built on, we went back, and half of all the buildings were gone. Split in half, clear.n We had floating lava blocks stuck in place. We decided to restart the world, and now all the buildings and the last 15 days of progress are gone, but the day counter remains the same. We also noticed that a few other things are gone, small buildings are gone completely, and it didn't reset the chink, just the buildings on top of the terriforming. We're not faking this. Could you share your insight on whether this is a glitch? Because I'm in so, sorry this is taking me back to the Minecraft Herobrine days. I added an image with a small circle showing where we were afk, and then a large circle showing the disappeared buildings. Is it like it's wiping the world left to right? I've already googled it, and nothing came up. Any insight would be loved.

world image with circles on inportant stuff