Hello Henry,
If the AP itself is showing successful adoption to the VX from the AP CLI "show adoption status", then issue could be with the rf-domain for this AP. Is this AP remote or local to the wireless controller? If remote, does the AP rf-domain have control vlan enabled and defined with correct VLAN (remote site VLAN AP is using to get out)? Are APs adopting over L2 or L3? If remote, are APs configured for MiNT L2?
If issue is still persistent, it may be best to get a support case open with us in order that we can review the configs.