The grandmother memory loss absolutely hits with me. I don't want to psychobabble and misattribute things but relationships with me tend to suffer that short object permanence effect - if I don't see a friend for a few months they'll often just fall off my radar entirely... until I see them again and the memories will rush back. I have a good friend with ADHD and we meet up maybe once a year - they are an extremely close friend even if that doesn't seem to make sense... but when I walk into a coffee shop and sit down with them we'll talk for hours and usually end up getting kicked out when they close.

This hurts (kind of, it's guilt driven hurt) when it comes to grandparents or other people who have passed away... if they come up in conversation or because of some related strong association I'll think of them and have a little bundle of memories that have weathered the years. But, like, my father passed away only two years ago or so and I rarely think of him - so then I feel guilty for not thinking about him more often and cry (as I am now) but give me an hour or two and he'll completely fly from active memory again.

I have no idea if neurotypical people are being genuine or performative when they say "Not a day goes by when I don't think about them" but that's absolutely not my experience.