Sounds similar to our issue we've been having throughout the year.  We first tried enabling QOS in SSID traffic shaping with default rules (which prioritize voice) per Meraki Support.  That didn't work.  The issue was our firewall (and typically is in most cases).  We have a Fortigate and by default it has a UDP Flood protect enabled under IPv4 DoS Policy.  We had to adjust the threshold to a much larger amount.  No wifi calling issues after.  The other issue which really can't be resolved is forcing wifi calling as a priority on the devices.  On Android you can set priority, not on iPhone.  ... View more