Tips to improve wireless scan?

My Trendset 692GR router will not connect to my ARRIS router at all, regardless if it's place 6 ft or 60 ft away.
In the past 4 days, it's appeared on scan once, and for just a few seconds only.
There was no issue until I upgrade to 19.07.2 - which wiped out my 5GHz radio as well.

I suppose one can assume that it needed the 5GHz radio to connect but if it has been visible once then I assume it can work with the 2.4 radio.