Possible bluetooth solution
I have good reason to suspect that my intractable iMac bluetooth mouse/keyboard disconnection problem was related to the Android File Transfer app downloaded from Android. Wipe/reload was the only cure until I re-downloaded that app. Never again!
I don't intend to waste any more time proving this, but wonder if anybody else agrees?
iMac (Retina 4K, 21.5-inch, 2017), macOS Mojave (10.14.1)