After so many attempts to get the "ask about peter" sequence to trigger on an old save (114 in-game days), can only conclude that its bugged. Tried everything forum searches have suggested and followed the guide to the "T" but it won't trigger. Already finished Amy's questline with 100 love/affection too. Also feel I've already done this "peter" questionnaire and talked about it with Amy on beach walk with version 3.5.0 or 3.6.0 but now its marked as not finished with the current 3.7.1 update. I even noticed that one of the "ask random questions" given to Alice, you find out Amy and Alice are stepsisters. Assumed this could have also been a hidden trigger, looped it with seeing Amy+Alice lesbian scene next day and then had a drink with Alice at the bar (no other girls present). No trigger leading up to the "asking about peter," only allowed to "ask random question/compliment" depending on red dress/black dress.
I've given up and started a new game. So far its working as intended following the guide and have not been able to duplicate frustration above. Positive its a bug for old saves. Shame. Lost a lot of unlocked images, did the whole sprained ankle scenario, unlocked the other two scientists, had Amy affection/love quest line finished. Don't want to grind but here goes...again.