Twilight Forest is using ServerPlayerEvents.ALLOW_DEATH to do things when players die, like saving their items or healing them.
On FAPI, this event is cancelled by returning false.

In QFAPI, this event is delegated to EntityReviveEvents.BEFORE_TOTEM in QSL.
This event is cancelled by returning true.

The result of FAPI events are not inverted, so this cancels when it shouldn't, and doesn't cancel when it should.

This seems to also affect ServerLivingEntityEvents.ALLOW_DEATH from looking at the code.

Related issue: https://github.com/TeamTwilight/twilightforest-fabric/issues/135