Leaving realm and rejoining creates a new realm

My players are reporting an odd issue, where sometimes, when they leave the realm and join back, they are put into the same world, but a different version of it on a different inaccessible realm. The issue seems to resolve itself overtime, but it repeats every so often. From one of my players I interviewed, this is what they said when I asked them to repeat the process of doing this glitch:

"At first I was playing on the server, I left for 5 minutes and rejoined to a server where nobody was on except 2 other people. It’s the same server but it is backed up 15 minutes."

I have never seen a bug like this, considering last I checked- I don't believe we are allowed to have more than one realm if we're only paying for one.