Auto-attendants with Yealink desk phones

Hi folks, 

I've been testing the Cloud PBX, AAs and Yealink phones (latest SfB firmware) but have come up with an issue, here is the config:

• Users are signed-in on their desk phone and the Skype for Business for Mac App
• AA with service number in Ireland
• Options 1 and 2 on the AA route to call queues
• A call queue has been set up and gets its agents from a distribution list

All of that checks out so far, then I call the number from my mobile, follow the routeing and get to the call queue I want, but only the computer rings - not the Yealink desk phone.

I've done the following tests to verify things are working:

1. Called one of the users in the queue directly from the Skype App on my mobile to verify the desk phone rings, it does.
2. Called that same user using the direct dial number from the regular call App on my phone, essentially a PSTN call, it rings as expected.

So the user is contactable directly, but the call queue isn't getting to the Yealink and I don't know why!

Would anyone have any ideas?

Keith