We have a network of R510s with ICX7150-C12P switches, all controlled by SZ100 (version 220.127.116.11.496).
3 SSIDs, each in its own VLAN. One SSID is Phones, and wireless (non-moving) phones are connected to that SSID (and only those phones).
We are getting complaints that calls via those phones are breaking up, it seems that the connection never fully breaks, but the call goes silent and then resumes. Sometimes they report 2-3 breaks in 2 minute calls, other times 10-15 breaks. On the network part packet drops are visible. While in standby, on the Clients section the phones RSSI levels are displayed with about -52 dB, but as soon as a call is made it drops do -75 dB.
All phones are Yealink T42S.
All other equipment (eg. laptops, tablets, smartphones) connecting to other SSIDs work normally as far as we know.
I am not 100% sure on the AP side, we may have to turn on something similar to honor dscp traffic or to mark all traffic ingress from phone SSID with a DSCP value. If you don't hear back from someone from our Wireless team here, please open a case with support.