The plugin seems to be incompatible with 1.19, as you can see here with this log at server startup : https://pastebin.com/tTQErz4g

I'm running the first release of Spigot 1.19.

Ah, interesting. It could be a Spigot incompatibility, but Spigot did work last I tested.

I compiled the plugin using the Paper API as it worked a bit better with Paper when I did so, but that should be backward compatible with Spigot as well. But it does figure that Paper would work best.

Backward compatibility stuff can get weird sometimes.

Elevators is now working with latest build of Paper 1.19. Either it works differently with Spigot, or something has been fixed in their code.