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Seems that router model does have compatibility issues with Nest products. This thread relates to thermostats but I would imagine it's the same issue speakers. It contains lots of workaround suggestions and updates on router firmware that may be useful to you.
Also, Asus have this page now:
@davidking, thanks for assisting others.
Glad to hear that it's working now. Since this has been resolved, I'll consider this post as complete and will lock the thread in 24 hours. Feel free to start a new thread if you need assistance with your Google Nest devices and the community would gladly help.