Yealink T58W and Grandstream UCM6308 delayed audio on outgoing calls

[waltersjo]

We recently installed a new Grandstream UCM6308 running firmware 1.0.21.9 system. Our deployment consists of around 450 GRP2613 phones and 60 Yealink T58W phones. Incoming calls all function fine with audio both ways starting immediately after the call has started for both Yealink and Grandstream phones. For outgoing audio, everything functions fine on the Grandstream phones as well as running Zoiper on my desktop machine, but when calling outgoing on our Yealink phones, there is a 3 second delay before the outside person can hear our internal caller (our internal caller can hear the outside person just fine during these 3 seconds). After 3 seconds, the audio is fine both directions. Occasionally audio will work fine both ways on those phones, but 95% of the time we are seeing this audio issue. I have set the audio codecs the exact same on the Yealinks as on the Grandstreams where they are only using the PCMU codec, and this is also what is set on our outbound trunks. All Yealinks and Grandstream phones are on the most recent firmware. Any ideas what I might be missing?