I always recommend to use the search function on the forum before posting as in many cases the questions have already been answered.

Here is a reference: https://forum-narutoen.oasgames.com/page/show-post-26989-1.html

"The placement of the rankings for Cross Server is based on two factors. I have asked the team to make sure this information is correct. The first factor is the placement of the group in Normal GNW. The second factor that contributes to their cross-server ranking is total group power. Hope that helps. Only top 8 groups in Cross-Server rankings are qualified for Cross-Server GNW."

This means that even though you are first in Normal GNW, it does not guarantee you a spot in Cross-server, as there are two factors that determines your placement and only top 8 groups continue to Cross Server GNW.

~Jib