This question already has an answer here:
Let's say my 2 Google accounts are called Primary and Secondary. I chose these names to reflect their function: I almost exclusively use "Primary". But I'm logged into both (intentionally). Every time I open Gmail, the Secondary account is used ("is active"). Every time I switch to "Primary" (which works), but when I close Gmail and open it again, it's Secondary again.
Is this because of the order in which I logged into the two accounts? Or why? And can I fix it?
Note: I don't have this problem in YouTube.