TLDR; Problem seems to have been fixed, so thanks for everyone who have already taken effort to give me some advice to solve it - it´s great to notice BB community is full of helpful and friendly managers (and staff, of course!).
Thank you for your message Alonso. You certainly may recommend that, however, I´m aware many (if not most) active managers prefer to chat in BB Discord nowadays instead of BB Mail or BB forums, but for me not joining discord has definitely been a conscious decision and I do not feel tempted to join Discord at the moment - hopefully BB forums will stay active as well. You have a strong point though as situation is quite urgent. Or in fact was, because now that I attempted to send rosters problem seems to have been fixed for one reason or another (even though nothing has been changed on my part in terms of settings, used browser etc.), and sending rosters does take me to the schedule-page as it normally should - I´ll report back if problems persist, but for now it seems all good. So again, thanks for all for your help!
-Wagner