Hi! The Sage World Battlefield actually has a minimum player requirement and it is the reason why it will say, "We are sorry, the battlefield could not be opened due to an insufficient number of registrations. If you do not have enough players, you may need to wait for Cross-Server before being able to participate. Cross-Server usually opens to new servers at around the age of 60 days since server opening. It is not specifically cross-server only, but may require cross-server depending on available players to actually meet the requirement.

In the future though, if you do suspect that there might be a bug, you can actually head over to the Bug/Support section found here.

Here is a previous post that also addresses a similar question, found here.