No routerlogin Xr300!!

good evening!
my problem is that i can log into routerlogin!
i connected a rx300 bought on 10-11-2020 and put my connect box( Austria T-mobile) in bridge mode !! on the first day everything was recognized and i could log in to DumasOS etc.!
The next day the login didn't work anymore!! i'm on version v1.0.3.50 so i'm the last one!! have reset router win 10 and installed all updates to the latest version etc.! have tried different browsers but nothing helps! have bought new network cables but still the same problem!
as soon as i enter routerlogin i get a message from my browser that the page can not load! i have internet all there but i can't log into dumaOs!! please help me as soon as possible thank you!