I mean just load a save again at the point they moved in and play it from there if you have one. I understand what you are saying cause I did the same by completing every story except the mary event then I had to load up a save from the morning the parents moved in and played it from there again (Including the new events I had already finished).I think it's possible that I can't do anything 5 days after my parents move in, because my parents moved in 50 days ago and I 100%'d all their plotlines and all of everyone's plotlines except mary's? So they moved in too long ago to be in some sort of recently moved in state? maybe? mary's house appears but when I click on it, it says "I don't need to go there right now", at every single time frame on wednesday. morning/midday/evening all of them.
There is a possibly related bug though on wednesday morning when I enter the kitchen and see my parents in there (before I click on either of them) it says midday, but when I leave the kitchen it's back to morning (since it should have also been morning in the kitchen).... as such if I need to visit the kitchen before going outside to go to mary's house... I can't visit the kitchen wednesday morning because it literally does not exist for me in 1.4 starting off at a fully complete 1.3 save file. That's gotta be it I reckon.