When I was running Mavericks 10.9.5 on my Mac Mini Server my bluetooth keyboard stayed connected during startup and restarting. My bluetooth keyboard is within a foot of the Mac Mini Server.
When the login screen appeared I may have waited a few seconds for the bluetooth keyboard to connect. The icon showed a full signal.
A couple of weeks ago I upgraded to Yosemite 10.10.2. At first the keyboard would lose connection from time to time. It continued even with new batteries. I noticed that the icon shows a grayed out signal with three black dots. The keyboard is in the same location. I also started having problems with the keyboard disconnecting when starting or rebooting my computer.
I contacted Apple several times about this. I went through different things including putting new batteries in the keyboard and going through steps to unpair and have Bluetooth rediscover the keyboard. This got me to the point where the keyboard quit disconnecting while using it. However it did not solve the problem when I started or rebooted my computer. I had to turn off the keyboard and turn it back on to get it to connect.
I contacted them again in utter frustration. The specialist walked me through a SMC reset followed by a PRAM reset. It works from time to time. However the last time I rebooted my computer I had to turn off and turn on the computer again. They also sent me a link to what could be causing problems with bluetooth. None of them applied to my situation.
The only change in my setup is the upgrade from Mavericks to Yosemite.
Has anyone had this problem and was able to solve it? I'm submitting this question because all the solutions I have seen online I have tried but still have this problem.