I got this email from a player on our 1.12 Spigot server, shortly after updating to 1.12.

we seem to be able to pvp by default. and /pvp off doesn't work.

I'm thinking it's maybe just that the plugin hasn't been updated to work with 1.12 yet? It says here last updated November 2016!

PVP is set to "true" in server.properties.

I've sent the bug reporter the link to this issue so that they can communicate with you directly if needed.

The friend who reported the bug investigated and found that I should use the .jar from this page, which I have now done, and the issue is resolved. :D Sorry to bother you!