When you connect via finder, it's from the sidebar? That reminds me of bonjour, have you reviewed this article - Fix Wi-Fi Problems in OS X Yosemite | OSXDaily
Especially the following section but I would try each one of them.
If you feel you've exhausted all options, contact back the senior advisor you've spoken to and request for it to be escalated to the engineering team, he/she should request to capture data of your mac to be sent over to the engineering team for further investigation - Best to do it while booted to the clean OS so that they don't have room to blame your 3rd party softwares installed.
I have already read that article and tried some of them, as I said, some worked but for a while.
Apple senior support even said the first method (deleting system config) is wrong and I shouldn't do that.
restarting of discoveryd worked, as some other methods, awhile.
I already lost patience with Apple support, these guys basically can't help anything unless you are really a newbie to OS-X. They never read Apple discussion forums, they are never aware of any 'hot' topics discussed by users in their forums and internet, once you call in, every advisor wants you to repeat the damn issue again and again even you provide them previous ticket number... I have contacted them before 2 times for some other issues, they sent me app to grab data and uploaded to Apple, and... that's the end of my ticket, no email or call follows up. I was told by a senior support that Apple Support Team has NO relationship with Apple engineer. I think those technical issues that Apple Support team can't handle, will be simply filed, only.
