Hello,
Your problem is very specific to GMMN and those particular spots. Looking at the AFCAD, J6 is a heavy gate and B3 and B4 are medium gates and are all very close to one another. Since J6 has a very large radius comparted to B3 and B4, GSX thinks that you are at gate J6 when you are actually parked at B3 or B4. Also, J6 has no SODE gate assigned to it so GSX will say "No Jetway" when parked at J6. There are other gates at this airport with the same issue. Without modifying the AFCAD, there is no easy solution to this issue. I would just use SODE at B3 and B4 to operate the jetway or just park at another spot that does not have this problem.