this has never appeared to me before and i played friendly cups pretty smoothly. i even deleted many invitations to have schedule relatively free, but i still got this nasty message.
i can not have fully open schedule for friendly cups, while it takes some time to have invitations confirmed. to manage good way the invitations finally I decided to quit playing friendly cups, while i constantly annoying message and I was not able to join it. the best is combination of friendly cups and friendly matches ... but no idea how now to make it under current message

I believe I was not stopping any cup, but currently i was unable to join it.
I propose firstly to get the explanation how it works now, secondly update it the way - the people who played it smoothly before could join them again even having not empty schedule.