Bro A.S.U. is linked with dBm, just like higher dBm means poor Network connectivity, a higher A.S.U. implies good network reception.
But they both tell you the same thing you don't have to look for both, you can check your network connectivity by seeing the dBm value alone. Don't believe this fekusupport guy, he is spreading false information.
And according to your Screenshot your device does have a problem with the network reception, if its happening frequently you should get your device checked