Domain users mush enter username &password

Question

i have sophos xg135 ver SFOS 17.5.8 MR-8 and domain controller, until last week users can access internet without capitive portal (as they appear in domain logs and STASS) and non domain 
 users can use captive portal. 
 suddenly today , domain users can't access internet without user portal every time. 
 
 note: i downgrade sophos version from MR-9 because it solve another issue that user must enter his username and password every 5 to 10 min.

mohamed hamed2 · Accepted Answer

Thank you for your support, i checked it and i remember that i delete domain user from sophos manually then disabled it in my active directory users and computer. 
 
 i enabled it again then this issue has been resolved.