Another annoying sizing question (sorry)

Hello! Sorry for another annoying sizing question but i've either been wearing wrong size shoes all my life or i'm doing the measurements wrong.

All my life i've been wearing EU size 38 (Female) training shoes. But when I follow HOKAs measurement guidelines (measuring the length of the foot) it falls under 25.5 cm which is 40 2/3 EU size lol. Had the difference been 1 size I would be okay with it and order but from 38 to 40 2/3 it seems a bit drastic.

I'd even believe I've been wearing wrong size shoes all my life, but it's not only the training shoes. The heels, sandals, I always have 38 and if I wore something bigger than that I would visually see they are bigger, it's much easier to see in sandals and open toed shoes.

So, I measured 10 times by now I'm going crazy. What am I doing wrong?