Last location causing bugs with teleporting between worlds and nether (no multiverse nether installed).
I went to the nether in world, then teleported to builder, and it teleported me to world - after teleporting to builder again i was in the nether. Had to disable last location.

Additionally one of my players found out that water pushing an armor stand still goes through nether portals which means users can bring armor and weapons between worlds using the nether.

Looks like an issue with your grouping. Please follow the issue template and send your server logs and config.