We are always working to improve Auto Attendants and Call Queues in Skype for Business, and we are excited to tell you about the latest features and updates rolled out in General Avaliability in July...
Updated Aug 02, 2017
Version 3.0
Blog Post
Vagish Bhatt and Greg Glockner - please contact Support if you see that Mobile and Mac clients are not ringing Call Queue calls, and also encourage you customers to open a ticket with Support as well. There is a great variety of network setups, and more data will help Support with toubleshooting, and they might also suggest a workaround/fix, if relevant.
Also, please note that we currently support only purely Online SfB users as Call Queue Agents - CCE users and users homed on Prem SfB/Lync deployments are not curently supported at General Avaliablity level.
As for Agent Opt In/Out feature disussed on this thread (Agents can temporarily opt out of having calls from a specific Queue(s) been sent to them), we get a lot of customer feedback consistent with the scenarios you are describing (thanks for the drill down on the corner cases!), so this is firmly on our radar (though there no ETA I can share).