Sorry, I skimmed your first post and didn't read thoroughly enough - so I think some of what I said in my prior post is inaccurate too. But, it still sounds like you're trying to piece together a network with what you have on hand, and it's resulting in some undesired behavior.
I don't think the age of the "access point router" has anything to do with it. I wouldn't recommend replacing it with the same router as your "main" router, unless that model is set up with ability to chain together multiple to "bridge and extend" another router.
Not sure if you're just new to Unraid or you're new to servers and Linux in general - some people start in this hobby by running an extra laptop with an external hard drive, fast forward 2 years and they're running a setup like this guy. So if that's you, maybe this is an excuse to level up your network hardware 🤷♂️😆