I just came by a very useful list of mods that are known to cause problems with the event.
https://scarletsrealm.com/grim-reaper-reward-event-mod-issues/
Avoiding these mods makes sense, though playing without mccc feels weird for me.
The real problem is what is mentioned next.
Pausing, saving and exiting the game will break the UI. As someone with limited time in the game that's a though one. I don't know if I will be able to complete every step in one gameplay session. Going to CAS or a loading screen can also cause problems as well. This makes me wonder if this event was tested before launch. Being able to save and close the game and continue at a later moment should be a basic functionality.
I am glad the first week went well but I will keep these things in mind next week.
You can play with MCCC, just turn off the setting that pauses the game when you load into a new zone.
To be fair, I played yesterday with that setting on, went into CAS with the full edit mode cheat, exited the game and returned later without a problem. So there must be other factors involved. Occasionally after doing those things, the event actions went blank, but popped back in seconds.
I did have a postal worker waving at my mailbox for most of the day, but it was after I got my newsletter. I don't have the NPC mod that is supposedly causing problems. I also checked and the mailbox is located correctly "in the green". So I don't know the answer for that one. I also had a last exception when the event ended.
I will make sure next time that the MCCC setting is turned off so the game doesn't pause on loading.
