When digging blocked really fast (Haste 2 Beacon, Efficiency 5 shovel or pickaxe) blocks will re-appear extremely often. I have attached a video to this report where you can see some of the blocks re-appearing. (sorry for the low quality, had to compress the file to attach it)

This bug is extremely frustrating when trying to clear out large spaces and completely defeats the purpose of having a Haste 2 beacon and Efficiency tools as it may be quicker to mine blocks slower so that they don't re-appear.

I know that my internet is not the issue. 

Please look into this, it is game-breaking. My friend pays for our realm and the current experience is not worth paying for in my opinion.