Title explains the issue.
Bloodmoon version 1.5.1 (MC1.10.2)
forge-1.10.2-12.18.3.2254-universal
Sponge is included on the server. (spongeforge-1.10.2-2254-5.2.0-BETA-2254)
Lots of other mods but i dont see why they would cause issues, but they incl foamfix, surge and betterfps

Probably should note this is with vanilla beds, and that the message "You don't feel tired enough to sleep" still pops up.

So can you reproduce this with only the Bloodmoon mod installed? (Without sponge)

With a friends modpack we have this issue too, the morpheus sleep mod (and possibly quarks sleep feature too) does some weird stuff that makes cancelling PlayerSleepInBedEvent ineffective.

I have an invasion mod that I've been testing a lot recently that also prevents sleep during some nights, here is my workaround to the problem, basically kick them out of bed if they somehow get into it:

https://github.com/Corosauce/HostileWorlds_Invasions/blob/1.12.x/src/main/java/com/corosus/inv/InvasionManager.java#L154-L165

Tested with many players, works great!