As soon as I run /lp verbose on I get these statements repeating over and over on the console making it impossible to verify in-game command issues.
[07:44:19] [pool-3-thread-1/INFO]: [LP] VB > [I] defaults/default - griefprevention.flag.entity-spawn.minecraft - undefined
[07:44:19] [pool-3-thread-1/INFO]: [LP] VB > [I] defaults/default - griefprevention.flag.entity-spawn.minecraft.monster.skeleton - undefined
[07:44:19] [pool-3-thread-1/INFO]: [LP] VB > [I] defaults/default - griefprevention.flag.entity-spawn.minecraft - undefined
[07:44:19] [pool-3-thread-1/INFO]: [LP] VB > [I] defaults/default - griefprevention.flag.entity-spawn.minecraft.monster.skeleton - true

• Pokecube Core: 1.12.2-6.34.13
• Pokecube Revival (if applicable): 1.12.2-6.14.2
• Pokecube Mobs (if applicable): 1.12.2-4.4.7
• Minecraft: 1.12.2
• Forge: 14.23.1.2587
• SpongeAPI: 7.1.0-SNAPSHOT-eebceb6
• SpongeForge: 1.12.2-2555-7.1.0-BETA-2831
• GriefPrevention: 1.12.2-4.3.0.511

okay, just opened issue with LP to see if he can figure out what might be going on. Thanks!

I honestly have no idea what would be going on here, I have never used GP or LP, so you would need to ask about this in their discord or issue tracker

LuckPerms says its a GriefPrevention issue, so just created the bug for them to look at. https://github.com/MinecraftPortCentral/GriefPrevention/issues/568

I got some grief from the GP developer and was told to create a new server install and start over basically cause he couldn't reproduce it on a vanilla install and wouldn't provide any other support until that was done. (not helpful at all)

So I did just that and went through the same steps at creating a new Pokecube Revival world. Adding only the mods I needed to reproduce the steps.
Here are the steps taken: https://pastebin.com/yQsm73eA
Here is the startup log from the console: https://pastebin.com/h55Uih8m

I went thru the portal after adding the poke*, thut* mods, I got a bunch of errors shown at lines 185 - 401 in the logs around the duplicate move of a pokemob. I went into creative mode and flew up away from the mobs. Then left the game (in air) and came back in. I of course then fell from a high place and died. The result was nasty on the server too. lol

So the issue doesn't appear to be my world or the other plugins, but perhaps a couple other issues that spurred it? I think I have to get past these issues first before I can say GP has an issue with Nether Portals. At least if I was him, I'd want to make sure no other issues were causing his mod to fail in the process. What do you think?

that is possibly a different issue, you need to update to Pokecube Core 6.36.0.b on the server

It does however still have cases of SpongePowered/SpongeForge#1810 occuring, so it seems that issue is still around.

Okay thanks - actually, that is the build I'm using on the server.

Oh, then it isn't what I thought it was, it probably is some sponge issue then... I suspect it is that issue I linked above for sponge then.

sounds like it yes