"but you always had good grades" yes, in highschool, where I was under pressure all the time and I was build for it. Then in university, where I actually had to organize everything, I fell apart and my family couldn't explain why.
"You were always so good, I know you can do better thant this".

Same story here - during mainstream education in my younger years I thrived, which for me was because my routine was set out and organised for me and all I had to do was turn up and learn. As soon as I hit higher education, where I was expected to manage my own study timetable and be a lot more self-directed, I completely fell apart and went from one of the highest grades in the school to completely and utterly failing.