OzarkEdge
Part of the Furniture
I suspect that the more recent ASUS routers (like AC86U) are not affected by this bug.
Also, I suspect that in a well-designed router like the AC86U you can safely disable UPnP and not impact Chromecast functionality.
As a test, I disabled UPnP on my AC86U (firmware 45149) last night, and was able to use my Chromecast and Google Home without any issues.
I have disabled UPnP on 66U, 68U, and now 86U... Chromecast 1 and 2 have always worked ok.
OE