I had the opposite experience, once you grind problems on leetcode and figure them out yourself, you somehow never forget them, esp under pressure in an interview. The problems aren't exactly the same of course but like Polya's book "how to solve it" describes solving a problem by considering something similar you solved, when presented with some interview problem to work through the first things that came to my mind each time were previous silly leetcode solutions I came up with that bought me some time instead of blanking out.