@Arzekial
While I was floating around the internet looking for ROM mods I came across info and a fix by Zero which sounds similar to what you are talking about as I too have noticed some changes of flirty behaviours where sims that do not know each other begin to flirt prior to engaging in normal conversation when they meet. I am not sure if this is exactly what you are experiencing but Zero describes this as follows:
it's called Fix For Mods that remove Idle Chatting
This is what is being experienced by her and other players:
They arrive and try to start the conversation being affectionate right away with sims they don't know. That first interaction gets skipped, the next in line is the Idle Chat. By removing the autonomy from it, in any way, the ability to start a conversation for NPCs is removed, too.
here is the link to the post and the fix
https://www.patreon.com/posts/fix-for-mods-30431338
There are also mods for no flirting and/or being happy if you require the auto flirting out of your game if you don't mind using mods.
https://www.patreon.com/posts/no-flirty-30676752