I reported the same issue I've reported since Day ONE of El Capitan...
Lack of support of allegedly supported Double sided USB to Thunderbolt cables.
These cables often cause the entire Bluetooth and Thunderbolt connection system to just shut down.
That means no IPhone, no Bluetooth until the Mac is completely SHUT DOWN. Reboot won't even fix it.
This is very annoying after buying an Apple Supported cable that crashes virtually your whole Mac daily. Apple doesn't seem concerned because it's only 3rd party to them, but I'm pissed about all these reports filed to no avail.
The inability to upgrade to El Capitan successfully is also a major problem. The migration program scrambles your email database. I lost email server info, accounts, emails, etc, etc etc. This has never been fixed and I've never found a way to upgrade perfectly from Mavericks or Yosemite without my MAIL being severely damaged. This is why I keep both other operating systems on my Mac Pro.
Also FaceTime still doesn't accept my Apple ID. Everything else does, but not FaceTime. Dunno why.
I still tell people. If everything works fine in Mavericks and there is nothing you want in Yosemite or El Capitan, don't upgrade.
As for Yosemite, that was an Apple disaster for me. It would always boot to a blank TV display instead of my Mac display. Just a terrible release that should have never happened.