Idk. My grandfather passed from Alzheimer's and looking back on it. He never really called me by name even when I was a kid. I'm not sure he was always 100% exactly sure who I was, but knew I was cool. Looking back he may have been coping with some memory issues for a long time and it just got untenable.
But yeah, he's definitely been like this for a while now. This whole second term kinda. All the nicknames and stuff, might account for some subject changes.