@TimothyLambert 2 things here... What DNS Servers are you using? Use CloudFare or Google DNS. Also by chance, do you know the signal strength of the clients that are having issues?

@TonL Have you tried a new cable between the cable modem and the WAN port of the router?

@TonL What are your wan settings? DHCP, PPPOE?

@lukass2000 Sonos can cause a multicast storm that floods the switch... that in turns fires off STP. I Would try to turn down RSTP to STP and disable loop detection. Sometimes RAPID fires off too...

@camp_ben Whats your "Limited Usage Counts" set at? Its defaulted to 1, May want to try 50? See if that helps?

@JCUK Have we confirmed that your wireless clients have good signal? Moving from Home Grade Wireless router to Enterprise APs is a completely different ball park. In wireless range, power, and...