When my wife and I (both Iphone11) select our Archer C4000 in the app it attempts to connect then returns the error: "An error occurred. Please try again later." Started over a week ago. I put off updating then once I did I got this error. 
 

Over the weekend I was able to add an "unknown router" and then request the webpage to sign in to access the parental settings, but this morning that disappeared and I'm back to the "error occurred" message. 

We had grown dependent on the app this summer and really want it back. For now we will set schedules via laptop login but I loved being able to turn on the Xbox when chores were done. Tyrannical, I know. Mwahahaa.

If the app doesn't fix within a week we'll probably goto Costco and get another router.