Quest items broken

[apffee]

I'm in a multiplayer playthrough with my friend and during it several quest items haven't been recognised. For example we had Madeline's Ledger but the quest objective to 'punish the wicked' didn't register that we already had it and couldn't give it to He Who Was.
After that we ignored the quest, unable to do it, and moved on.

But at the Gauntlet of Shar we put all 3 Umbral Gems into the thing to unlock the door but only one visibly appeared and the game behaved like only that one existed and refused to open the door. We opened it with Knock but now Shadowheart says we need the spear of night even though she literally has it equipped.

We tried turning off Mod Fixer, then tried replacing it with Script Extender, tried disabling all mods and leaving it in the library where we reloaded and picked it up again. We also tried putting it in a camp chest and even tried spawning it in. Although using Feign Death on Shadowheart and bringing her into the Shadowfell gets us past the part where she demands we need the spear, but this problem seems to affect any quest items.

Does anyone have any solutions? My friend's at his wits' end T^T