Adriaan Renting

I am getting the same errors on 1.20.1 after upgrading from 1.7.10

I have never ran any mods since 2010, this map is from around 0.9-1.0, shortly after the change to sea level height.

I was unaware of this problem and we lost the stats of several players when we updated from 1.7.10 to 1.8.4
The server hadn't run for over half a year.

The server is running Ubuntu 12 with:
java version "1.8.0_05"
Java(TM) SE Runtime Environment (build 1.8.0_05-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.5-b02, mixed mode)

I've had this issue when updating our old server from 1.7.10 to 1.8.4.
The server has been around since early Alpha and the current map since Beta.
It's had a lot of players over the years and there must be several hundred portals. Relighting them and fixing any extra that spawn is going to be a major chore.
I'm very surprised that this hasn't been fixed since 1.8's release.
Currently running 1.8.5

This just happened to me on Minecraft 1.8.5
OSX 10.9.5 Mavericks. 8 GB, 6750M video, i7
java version "1.7.0_21"
Java(TM) SE Runtime Environment (build 1.7.0_21-b12)
Java HotSpot(TM) 64-Bit Server VM (build 23.21-b01, mixed mode)
I was logged into a server also running MC 1.8.5 on Ubuntu 12, although I think it's got nothing to do with it.

It does seem to be related to Command-Tab and/or switching between Minecraft and other applications.