I paired my Varia Vision (FW 3.50) to the 5x Plus (FW 4.20) today to try it out on a casual volunteer ride. Easy pace so lots of time to play around with gadgets.
It paired up fine, I scrolled through a couple screens and seemed like it would work at least as good as my 5x. But as soon as I got started on my ride I noticed my HRM4 has dropped (This never happens) The HRM4 would not reconnect until I turned off the Varia Vision sensor in the 5x Plus. Strange, but I had similar problems at various FW levels early on with the O.G. 5x.
Note: I also has a speed and cadence sensor on at the time, but I did not notice if my other sensors dropped out.