So, I'm coming back to this one here. It's still happening.
I gave it another try with Cottage Living after I moved out and lived in a apartment in San Myshuno without farm animals and now I came to a conclusion.
Your farm animals definitely cause something to mess up with Grim. And this also happens without any mods installed.
Approximately once your third or fourth chicken dies(don't know if this applies to cows too), something happens with Grim. He won't lose his Soul Reaper Status and he can't be interacted with. (Again...)
On my end he even initially refused to reap my chicken, who was in "One...last...pet..."-State but I had mods installed by then and after updating some, it got a bit better and the chicken was reaped.
But then the curse continued.
You can load out of the lot after he reaped and load back in to get rid of him (similar to what I had done in Evergreen Harbor) but this is now the second time this happened.
And now the worst part: It happened in Henford - on - Bagley. Great, the town where the DLC plays in is cursed with this bug.
So...once you are affected by this issue the only option is to move out of there and let some time pass.
It seems like Evergreen Harbor was partially fixed since Grim still doesn't lose his Soul Reaper Status. however he leaves immediately after reaping so that's something at least. However it seems that this curse now spreads to other worlds. San Myshuno is now also affected even though I never used farm animals there.
It's a shame, I moved out from my apartment in San Myshuno because of another bug and now I have to relocate once again just because Grim isn't functioning.
Yes, I could just deal with it and keep going but do I really want to go through these already long loading screens everytime, just because Grim won't go on his own? I don't think so.
Sorry, I had to rant. This has gone for far too long now. How about EA and Maxis finally wake up and take a look at this issue before even more experiences get corrupted.
Let me guess...once we get horses with new pack, they will get this issue too?
And just where I actually loved the way of playing with Rustical Living. Harvesting Eggs and Milk by myself. Going shopping just like I had to in The Sims 3 for cooking and now...this...
So one word of warning. Never let your farm animals die or better yet don't even bother getting any until this issue is resolved. Or else you will definitely either have to relocate your sims to another lot or deal with a Grim Reaper who just won't leave you alone after reaping the souls of the dead unless you leave the lot for a while.
I'm actually quite infuriated by now. This has really gone long enough.