You need to call CombatLogGetCurrentEventInfo() inside CLEU event to get the combat log payload nowadays. (You can also get the destName from here instead of using unit GUID, which doesnt work for unit ID functions, but destName/srcName does aslong as they're in your raid.)
Idk if its a typo with the elseif event, but "SPELL_AURA_REMOVED" is the sub event from CombatLogGetCurrentEventInfo(), not main event just incase.
Also unless im too tired, spellID is the 10th argument not 11th for UnitDebuff.
Where do you call UpdateRaidDebuffList?
See
https://warcraft.wiki.gg/ for latest up to date API documentation. Other sites are outdated.