Netgear mr60 mesh - Amazon echo issues

I’m having problems with my mesh WiFi and Amazon echo devices and wondering if anyone can help please.

I’ve always had issues with multi speaker groups on Alexa with them intermittently not working but now I can’t even get the Alexa app to link any of my devices into a multi speaker group at all.

I used to have a separate router and my MR60 mesh in access point mode but have just had full fibre to the premises installed yesterday so have now started to use my mesh WiFi directly connected to the openreach box via an Ethernet cable. In effect I have no separate router and my netgear mr60 mesh is all I use for my WiFi.

I’ve tried connecting my Alexa devices to both the standard mesh wifi and also the guest network. Individually each echo speaker works fine but whenever I try to use the Alexa app to combine them into a multi device speaker group I can select one device but get a message saying network error when I trying add either of my other two devices that are on the same WiFi/guest network.

In the past Amazon have told me I needed to have TCP ports 55442, 55443 and UDP port 5544 open for use on my Lan. On other routers I’ve had in the past I’ve been able to open ports like this but I can’t see how to do this on the mr60.

Has anyone else managed to combine amazon echo speakers into a group on this kind of netgear mesh? Does anyone know how I could open ports on the mr60?