Firstly, a little background info:

I have about 10 cast devices, mostly Google Home's and I have a Virgin Media Superhub 3.

Due to the WiFi signal not being that amazing, and after reading some goog things, I've just got an Archer C9 unit.

I set Virgins Superhub 3 into modem mode, and set up the Archer device, and all seemed to work fine, and WiFi signal is better as I had hoped.

However I've not been struck with an annoying problem as follows:

I enjoy listening to podcasts, and "Cast" the audio to my Google home devices, and other cast devices on the network.

The programs I currently use for this are "Pocket Casts" and "CastBox" and I have these installed on 4 different devices. Two phone and Two tablet.

What I find now (and seems very odd) is I open either of these apps, and the CAST icon does not show up right away.

Perhaps after 15 seconds it will show up, but then, maybe only 1, 2 or 3 of my cast devices will show up, if I wait, the list may actually go down to only 1 device!

Then if I want longer, perhaps a minute or more, then all of a sudden they will all appear and will work fine.

Once they have appeared, I can close all apps, wait 10 mins, and try again, and they are all still there, as if there is no problem.

But if I wait quite a while, then try again, again the icon and items don't appear again.

It's almost as if, it all goes to sleep and takes a while for the cast icon and list of devices to wake up, and once awake they stay awake for a while.

Bit if I leave it too long, it all goes back to sleep again.

It's not the device I'm using, as I can use my phone or my tablet, and both devices, can only see the same list of cast devices.

It's as if the Archer C9 is not making the list availiable?

Following some advice, I set fixed IP addresses to each of my Cast devices, but that has made no difference.

I've changed WiFi channels, but also that has not made any difference.

Is there any other setting I can change/edit to resolve this issue of the Cast icon, and list of cast devices, seemingly going away/to sleep and taking ages to appear and be available from the router?

Many thanks :)