1.16-pre5 Mismatch in destroy block pos: Not able to mine blocks, open things in spawn area

Trying to break blocks or open doors / chests within the spawn area doesn't work.

Block breaking attempts result in a message on the server:

[10:05:17] [Server thread/WARN]: Mismatch in destroy block pos: ft{x=0, y=0, z=0} ft{x=-30, y=63, z=-214}

Background: After the recent launcher update which took our desktop version to 1.16-pre5, we noticed one of our computers can no longer open or mine things very close to our spawn area.

The server was on 1.16-pre2, we attempted to connect to the pre-2 server with pre-5 clients (which obviously gave us the message that the server was downrev). We set our client back to pre-2 and first noticed the issue - but it's possible the client version stuff is nothing at all to do with it.

I decided to roll everything forward to 1.16-pre5 on server + client, and the issue persists. 

Interestingly, My account is fine - but my son's is not.

The changes made since it was working are:

• I had to add in the end portal location array in level.dat to deal with the End City portal not appearing after killing the ender dragon (using NBT explorer)

• I made myself a server operator (my account still works fine) so I could /kill the enderdragon to test the portal (which worked)

• I did not make my son a server operator

Result was the issue with the one computer (the non-op'd account) can't open stuff, or mine stuff around spawn. 

Also of note is that if I make my son a server operator, he can open things, and mine blocks around the spawn area, and if I de-op myself, I can also not open / mine things around spawn.

When the not working account tries to break blocks, we get messages like: 

[10:05:17] [Server thread/WARN]: Mismatch in destroy block pos: ft{x=0, y=0, z=0} ft{x=-30, y=63, z=-214}
[10:05:17] [Server thread/WARN]: Mismatch in destroy block pos: ft{x=0, y=0, z=0} ft{x=-30, y=63, z=-214}
[10:05:29] [Server thread/WARN]: Mismatch in destroy block pos: ft{x=0, y=0, z=0} ft{x=-34, y=63, z=-218}
[10:05:29] [Server thread/WARN]: Mismatch in destroy block pos: ft{x=0, y=0, z=0} ft{x=-34, y=63, z=-219}
[10:05:29] [Server thread/WARN]: Mismatch in destroy block pos: ft{x=0, y=0, z=0} ft{x=-36, y=63, z=-220}
[10:05:30] [Server thread/WARN]: Mismatch in destroy block pos: ft{x=0, y=0, z=0} ft{x=-37, y=63, z=-220}
[10:05:30] [Server thread/WARN]: Mismatch in destroy block pos: ft{x=0, y=0, z=0} ft{x=-37, y=63, z=-221}
[10:05:30] [Server thread/WARN]: Mismatch in destroy block pos: ft{x=0, y=0, z=0} ft{x=-38, y=63, z=-221}
[10:05:30] [Server thread/WARN]: Mismatch in destroy block pos: ft{x=0, y=0, z=0} ft{x=-38, y=63, z=-222}

We get no feedback at all trying to open chests / doors.

Cheers!

Nathan.