Bewitchment's coffinHack mixin, which redirects into an isDay check in order to let players sleep in daytime if using a coffin, is not compatible with other mods that modify sleep mechanics.

Haema used to have a similar issue; it used a mixin to the same place to allow vampires to sleep in the day, and this made it incompatible with the Comforts mod. I was alerted to the Somnus library in an issue report, and Haema now uses it, making it compatible with Comforts.

If Bewitchment were to use the Somnus library, specifically its PlayerSleepEvents.CAN_SLEEP_NOW event, it would be compatible with other mods which use the library to change sleep mechanics. (ideally Somnus would be incorporated into FAPI itself, but that's up to TheIllusiveC4)