Hey

From my own findings, Group Summons refreshes passives overall. If a passive barrier ninja remains on the field, it'll refresh his/her barrier.

If a skill was being cast prior to the Group Summon, it'll cancel.
It's an integrative strategy to use the group summon the second turn to absorb opponents mystery skills and re-apply passives after.

If that's not working as intended next time. Let me know
If you can record a video, that'll be great as well.

I'll test it out myself tonight as I have GNW.