Producer and director Naoki Yoshida has been doing his best to keep players updated, but at this point getting past this early instance is largely a matter of clicking for entry repeatedly and hoping to not get the now-dreaded error message stating that the instanced battle could not be started. It’s not exactly surprising that the game would have some issues with early access, but players are left unable to progress beyond the first two areas of the expansion without some appreciable luck (and the instance servers aren’t at their most stable even for other purposes). The issue is being addressed, so keep your eyes peeled for updates when the logjam is finally broken.
Source: Official Site