if this is a persistent problem, then I think the ADHD explains a lot. The key I would hazard a guess at is to try and introduce some hyper stimulative properties to your practice days. Whether that be particular music or pretty much anything to break up the day. As you will know boredom is the worst thing to have. Sometime it’s better to do things differently to everyone else.
I know what it’s like to be slow in practise, and even the heats, and then come the final your bang on the pace. I had the problem for many many years until I started delving into various conditions and discovering where the possible roots of this problem were.
I can’t even read a book in the same place more than a few times or write in the same place. Need constant noises, movement, change of environment.