Memories disappearing (?!)

I, for one, adore that they optimised the automatic memories / notebook, whatever you want to call it. My characters had so much information stored there. I loved that!

Just now, I checked the memories of the character I was chatting with.

One subcategory (it was quirks, I think) simply vanished.
Additionally, key facts about a side character (like his appearance in detail, his occupation) are gone too.

This is happening despite the fact that it says that ‘Saved memory stories and facts stay untouched’.

Is this just a bug?