@Saltypaws Returning to your original question, I had this happen just once when one of my sims unintentionally died of overheating in the sauna.
The sim turned into an urn but Grim never showed up.
After installing City Living, I had a sim die at a wedding at Myshuno Meadows' Center Park and Grim took around 2 sim-hours to show up. No could leave the venue until he showed up.
In the past month or so, I get a glitch where a household sim dies but their portrait remains in the lower left with the rest of the household until the family travels somewhere then returns. The first time it happened, I wasn't sure my sim was dead or not. Since then, I don't panic and just wait until the family travels or I exit/reload the game.
So, Grim has not been very consistent about reaping souls for me, either. I remember
@Playalot having serious issues with Grim during the last two generations of her Hollingsworth Immortal Dynasty.
I'm curious what happened when your sim tried inviting the GR over to their lot.
As long as I'm not at Center Park, Grim has been appearing in a timely manner for the past 3 generations.
I checked at EA Answer HQ, but couldn't find any reports similar to your problem. Sorry, but I didn't find anything related to your problem.
Maybe
@MrsFlynn can tell you how to proceed?