Q: Bluetooth Hunting Blocks Access to Keyboard-Trackpad after sleep

I have a mid-2012 MackBook Pro (non retina display) running Yosemite 10.10.5. I have the problem many have, my Bluetooth keyboard disconnecting every few minutes, lags in typing, etc. I also have the (apparently also common) problem of sluggish waking up from sleep.

But here's a weird wrinkle: I open my MBP, which has been plugged in to the power adaptor with the lid closed through the night. When I open, the screen is blurred and the progress bar appears. But what's totally weird is that all my IO processes--keyboard, trackpad--are frozen. After a while, the Bluetooth preferences panel opens and informs me it cannot find a keyboard! Once I dismiss that window, everything works fine.

Any insights or links will help. I've searched the messages and Google, but I might have missed it.

Many thanks in advance!