on premise gateway not listed in Power Apps

[ryanbasnet]

Hi, 

I am not able to see on premises gateway in  Power Apps Gateway page and dropdown in connection wizard for gateway is also empty.
Its existing gateway which was working in the past. Even cross checking region or installing new Gateway did not help, though gateway status is online and listed in Power Admin Center.
Gateway age has "DMTS_UserNotFoundInADGraphError" , has any faced the issue before ? Would really appreciate the advise as its impacting the Power Apps and MS Flow that use Power Query. 
Thanks in Advance