This started after the patch for us. I am playing on windows 10 and Zenon Awful (husband) is playing on Xbox. This is his realm so it was created on xbox. We can only mine a few blocks before it lags up and sometimes we are inside the blocks when they respawn. Everything comes to a stand still for at least 30 seconds. 

In the first video you can see us digging out the side of the mountain and the lag happening. The blocks come back. The second video is 30 minutes later we were disconnected from the realm and when we reentered the realm everything was frozen and that entire cliff face was back. We lost 30 minutes of work. 

edit. i have video it won't let me upload them.