If simply not repeating a scene enough times, thinking I was done with an area, and advancing the story is all it took to get locked out... well that's garbage.
This is unfortunately happening now and then. And since I know that I feel pressured to repeat all possible scenes a day before the MC goes to bed, just to not miss something. You can even get new scenes with totally different characters, that you would have thought of.
For example the spirit festival. You can have a scene with two spirits there. Later you can repeat that scene and if you do, Ikki suddenly shows up and you can have a scene with her instead. In the current build you not only have to have fun with the granny, you also have to choose the right location for it. And only then you will get a totally new scene with Jorina and Ikki afterwards. This is totally unpredictable and unrelated, so you kinda have to do all the scenes in all variations and as often as you can, so you don't miss out on anything.
In your case, I would load an older save (before the lockout) and use the cheatcode to unlock loli content. I also got locked out once and did not know why, so I used the code and all is fine since then. I don't consider that cheating and I also don't really care outside of real gaming.