I'm using the beta 2 in 1.18.1 and the lights aren´t being removed after I remove the Feral Lantern.
https://ibb.co/Y8ZQCtb
I even used the item to remove the lights.

As always, fixing things a few minutes later x) (Thanks to mcjty's wiki)
Switched to saveAdditional() and it's working now, please try version 18.0.3-beta either from the torchmaster github releases or from minecraftforge (once approved by curseforge)

I've been looking into this problem, but I'm unsure what is going on.
Generally, this bug occurs after the tile entity has unloaded (i.e. due to a world restart or just chunk unload) - the BlockEntity::save() method is not called. I am making sure I call BlockEntity::setChanged() after placing a light block, but for some reason save isnt called during a chunk save.

I'll be looking into this when I find more time but if someone else has an idea, hit me up.