Hi L&LD, sorry, I missed your question. Ok, currently I'm using an RT-AC5300 as my router and I recently added an RT-AC86U as a node in an AiMesh configuration. Current on both firmwares, etc. Perhaps I should try this on a windows 10 machine?
@COBOL-Coder what router do you have again? What firmware are you running? I'm not logged into the GUI but the difficulty might lie with the fact that I'm using an Android (9) tablet with an Android browser.
Are you logged in to the router GUI when you try that link? If not, it should still ask for the login credentials and then immediately take you to the 'Restore/Save/Upload Settings' tab.
Have you disabled the ability to access the router from 'router.asus.com'?