I do not mean SPAG issues or things you consider bad writing/storytelling. What is something which is not actually a problem that you just don't enjoy to the point where you would drop a fic you were enjoying?
I was considering this, because if a premise interested me in the first place, the biggest reasons I could think to ever drop it would be too many grammar issues or characters suddenly feeling OOC (in my opinion).
Outside of those or untagged triggers though... I considered how I might actually stop reading a story that goes by too fast and doesn't let the reader explore characters' reactions to things. Even if the characters still act like you would expect them too afterward. I like diving into characters' feelings and motivations too much.
Massive OOC turns for established characters, or sudden tone shifts that don't make sense in the context of the story. I don't often mind OOC in the context of the source material but if it's OOC in relation to the rest of the story, that's a hard nope from me.
A sudden disappearance of any & all smut in an M- or E-rated story once a relationship is established. Gah!
Likewise, when pregnancy/children are portrayed as the pinnacle of a romantic relationship. I'm fine with babies/kids being part of the story but when they're suddenly pushed as the focus, my tokophobia & childfreedom start showing.
Apart from those, it's mostly ongoing obvious SPAG issues.
And sometimes poor tagging, although this is usually the case when I'm already finding that I don't like the story. If I've already been happily engaged with it, I don't really care so much about the tags by that point.
I don't have/want children myself, but I have no problems with them in a story. I can even enjoy them a lot. I certainly don't like it when it is portrayed as a necessity for romance. I do like reading about people discussing if they want kids at all, whether or not they decide to have them. Much as I like reading about most relationship discussions where the characters are opening up to each other about what they want in the future.
Oh, conversations about what people want from relationships, be they friendship, romantic, family, are great! I think they tend to come up more in non-traditional relationships IRL, whereas the run of the mill "heteronormative romance equalling marriage plus kids" dynamic tends to have very little introspection/interrogation of assumptions (this is totally my opinion). It's great to see when writers/creators bring those often ignored conversations into more traditional relationships on the page imo because they're inextricably linked to consent.