Issue with: b432 commit 9fbdb74
spigot version: 1.12-R0.1

b431:
Everything appears to work when swapping between worlds and world groups.

b432:
The default world/worldgroup inventory works perfectly fine, but every other world/worldgroup looses all inventory items, however players do not loose stats (experience etc).

I have tracked down the issue, and fixed it in the following pull request: #314