So I'm in league I created by myself as the only coach but during the offseason I can only advance days or through tasks as commissioner, not as my coach. Is there any way to change that? It's a minor inconvenience but it would definitely be helpful to be able to stay in the coach tab and still advance

Which MODE did you use when you created the association? If you used Universe or Multiplayer, then the way you advance is via the commissioner office. If you used Challenge or Sandbox, then something is wrong with your association and you need to submit a Support Ticket along with your game files.