None of their cams use Wifi 7 so that doesn’t matter. Most use Wifi 4, a couple now support Wifi 5 or 6 (in your case the v3 are Wifi4/N and the v4 is Wifi6/AX).
Repeaters are very problematic (if you’re actually running them as repeaters and not wired APs). Also do you really need 4 APs covering your space, how large is the coverage area?
Too much wifi can cause just as many problems, sometimes more, than not enough wifi.
That being said if icons are missing and the app itself is running slow and not just the camera feeds, that could be your phone or the app. Have you tried uninstalling and reinstalling the app? When you exit the app, are you fully closing it or just switching to another app and leaving it running (which will probably cause it to start to bog down and glitch).
Another thing to consider, if you have all 20 cams on your favorites with live stream enabled, that could be a heavy load at app startup, you can try going into your account settings and turning it to manual to see if it helps.
How old is your phone? I’m running a 4 year old phone with Android 14 and it seems to handle my 7 cams fine, even before I changed the streaming on the favorites screen to “manual”.