I was riding a long minecart track on my realm and decided to browse the marketplace while doing so, then after going back out of the marketplace back into the actual game I was in a whole different chunk. It looked like my realm but in 1.20. My realm was created in 1.15 but is up to date. I think it's like the error where you see chunks in the distance but normally, they would disappear before you could walk to them however, I was able to fully get out of the minecart and walk around. I have a video attached to this post.