Best way to troubleshoot wifi performance for Balance One or SOHO MK3

I have about 4000 SQ ft space divided into 3 floors, by drywalls and wood materials. I deployed SOHO MK3 deployed at the basement space and was hoping that should do fine for WIFI coverage. However, I noticed that MK3 wasn’t cutting it and noticed bad performance on the third floor and some edge rooms on the 2nd floor even though router/wifi is installed nearly the center of the house. I recently changed MK3 to Balance One WIFI hoping that Balance One may do a better job. It seems to do the trick then I noticed horrible performance issues again. Restarting the router or resetting the AP seem to address the issue then the issue comes back again. I did separate 2.4 and 5 GHz AP and it seems to do better for devices using 2.4., but devices using 5 GHz still have some horrendous connectivity issues.

Is there a good way to troubleshoot this at the log level? One reason why I separated the 2.4 and 5 GHz frequency was because I saw a lot of log entries where my iPhone flips between 2.4 and 5 GHz frequently. My old TP-Link WIFI did better job handling WIFI at home than Balance One or MK3 device. And I don’t plan to go back to TP-Link or Linksys product if I can help it.