Has anyone run into a bug where a quest doesn't complete, i.e one of the objective remains unfulfilled, even though it's done.
Specifically Cat upgrade 4 - I've got the armor schematic and even crafted the armor itself, yet the quest won't complete.
I even tried to spawn the schematic with the console - didn't help.

I have never seen that happen myself, but the first thing I would check would be to make sure you have all of the mastercrafted armor diagrams. For that quest, all four armor pieces should be in the same place (chest, boots, gauntlets and trousers). If you are missing one of those crafting diagrams, maybe it's still in that chest.

I did that. The chest doesn't light up. It's fully looted.