AD shares across site -- unable to modify.

Have domain with shares.

server 2016 - using AD.
2 sites
using dfs 

site a users can access share, modify and delete.

site b users can access but not modify edit delete

same user - site a works fine - users can create - modify - delete
site b cannot modify edit or delete

when i goto direct share on server still same behavior from each site. 

i have tried on different systems at each site using same user - site a  allows full access

site b does not allow full access - though permissions should allow this. and its same share through domain.xxx

even if i have site b access site a share directly -- \\server\share - its read only. 

if i have the same user on a site a workstation access site b via \\server\share it works as well. 

its only if i am logged into a workstation from site b that i can not modify file on the share.