Can't get Time Machine to work with Nighthawk

Hi all. Thank you for all of the information you've posted. My issue with Time Machine is that the router-connected drive does not automount when my mac connects to the router's wifi signal. While I haven't tried most of the steps recommended (as I was somehow already able to manually mount and start a backup to the drive), I'm stuck on step 5.

For starters, while I was able to connect to smb://readyshare through the finder "Go" menu the other day, I get an error now:

There was a problem connecting to the server “readyshare”.

The server may not exist or it is unavailable at this time. Check the server name or IP address, check your network connection, and then try again.

I am able to connect to afp://routerlogin.net (manually), but not with my credentials. I've tried every combination of username and password I can think of. admin/<passoword I set on the router> definitely does not work, even though it does work when logging into the admin panel at http://http://www.routerlogin.net/.

I am able to connect as a Guest and start the backup. The main issue I'm having is the automount. Even before reading this thread, I performed step 5g. However, after a disconnect and reconnect to the network, the window for that step shows two yellow triangles (can't figure out how to insert a screenshot here) next to the drives I want to automount on login. The help menu for that preferences panel states:

If you see a yellow triangle next to an item, the item won’t open automatically because it was moved or deleted.

I have to return to the Finder and again mount the drives through afp://routerlogin.net as a Guest.

Another oddity is that, when I first mount the drive, Finder tabs for both USB_Storage and T_Drive (which is a separate partition on the external HDD) automatically pop up, but they don't show up in the left pane of the finder window. All that does show up is a "Location" object called R7000P, which I assume is my router as that's the router's model number. When I click that object, the finder window shows no files, only a message "Connection Failed" on the top left and a "Connect As..." button on the top right. If I click that button, the two drives immediatly unmount and there is no prompt to log in again. I have to again go to the Finder -> Go -> Connect to Server... menu and again log in and mount the drives through afp://routerlogin.net as a Guest. This is driving me absolutely batty!! (FWIW, after remounting, when the finder tabs open for the partitions, I am able to do a Get Info on each one, and they show "Server: afp://routerlogin.net/USB_Storage" and "Server: afp://routerlogin.net/T_Drive" respectively.)

Any ideas would be very much appreciated. I tried tech support 2 days ago when the router spontaneously rebooted and wiped the logs during a video conference call, and after more than an hour of waiting, the support person concluded the router lost power due to inclimate weather. The skies were blue and clear. The sun was shining. The birds were chirping. And no other electronic device in my apartment--including ones connected to the same power strip--suffered any loss of power. In short, there's no way in helll I'm going through that again.

Firmware Version
V1.3.1.64_10.1.36

macOS Catalina 10.15.5