I have the same issue with Archer A7 1750.

Set up WDS, restart PC and then it recognizes the a7 as my main router, I cant enter the a7 settings afterwards unless I factory reset.

I was able to figure this out. I did start the process over though. One thing I did learn is that you do not want to direct connect the router to the internet after you have placed it into WDS Bridge Mode (advice that I got from someone I game with). This also means that you must direct connect to the router with an etherenet cable (or USB cable if you prefer) through one of the ethernet ports on the router & then copy and paste the new IP Address you assigned to the router into the internet browser. I tried typing the new IP Address in the broweser before, because I figured this was the case, but I could not connect to the admin page through the new IP address the first time I did it when I came here looking for help (not sure what was wrong). Obviously needing to direct connect means that if you are using a laptop w/o an ethernet port (which, most do not have now), make certain you have a USB-C port to ethernet or USB to ethernet adapter.

In the past, I used a ZyXEL Pass-Thru Ethernet Adapter 1800 connected to my modem, which I then used to connect to the 2nd adapter that was connected to my router in a different location in the house. It worked fairly well, but I was loosing a lot of speed through the connection; the electrical wiring would lose some speed along the way with interference or going through the breaker box or something.

The other advice I received here from terziyski was also solid.

I'm not too pleased with the speed this old C5400 is puling and broadcasting in WDS Bridge Mode, and it's only about 50 feet away. I may opt to direct connect this router using a 50 ft long Cat 7 cable I purchased and either run it through the foor and up the wall or up through the ceiling and down the wall to where I have this thing positioned. I also purchased a TP-Link Relayer to see how that works out. If that works well enough, then I might just put that 1 or another 1 in the tenant side of my duplex.

One question that I do now have though: Are you able to use the same SSID broadcast name for both the root and extended router? I did this, and it seemed as though there was a lot of interefernce. That being said, I don't like the fact that I have to switch the router I'm connected to based on my position in the house. It would be nice if my device could just choose the same SSID based on where I am in the house. (Guessing that this is just a downfall of using an old router in WDS bridge mode like that v. an actual repeater designed for this function?)

  @terziyski It certainly did not automatically name the SSID the same as my new Arris XB7 (TG4482A) provided by Comcast & when I previously renamed the C5400X the same as the Arris modem/router it seemed to cause a lot of intereference dropping the speed when connnected.

I received the new TP-Link range extender I purchased today, and didn't realize it would not be a OneMesh or similar mesh setup. Now I have an enitrely different Wi-Fi network. I guess that I should have researched this further and simply purchased the xFi Pods that are compatible with the dumb Arris XB7 & called it a day. I'd put the old C5400X in OneMesh mode, but it is apparently too old & does not have this functionality. Maybe I can return the TP-Link Range Extender that I just purchased to Amazon.

Only other options I have appear to be (1) put the new Range Extender in my tenant's side and just have her connect all of her devices to that (2) buy a new TP-Link router with OneMesh capability & put the Arris XB7 into bridge mode to just use it as a modem (3) return the Range Extender & buy the xFi Pods. The xFi Pods seem the way to go presently; othersise I don't have a mesh, and I'm continuosly changing which network I need to connect to based on where I am at.

  @terziyski: I again changed the SSID name on the C5400X to match that of the Arris XB7 and it seems to be working fine now. Thank you. It still leaves me with that range extender that would be on a separate SSID.

Thank you again

Now to decide if I want to try to run an ethernet cable to this old C5400X.