This is starting to drive me crazy -- or at least crazier than I already am
So after my last post (Dec 27/18) I ended up buying a wireless RF mouse with a USB dongle (Macally). And guess what, my bluetooth problems mostly went away! Happy me.
Then because I was having some other issues, I ended up installing 10.13.x (7? > .6 anyway). Then things went down the drain. After a reboot, bluetooth would work until the computer went to sleep. When it woke, nothing I could do would connect the Magic Mouse (or my Kensington BT mouse). So I started using the RF mouse exclusively, but while it is a nice enough mouse I really prefer the MM.
So I upgrade to Mojave (10.14.3) figuring it couldn't get any worse and things got better. The MM mostly works, but about 1/3 of the time about 30-60 seconds after waking it disconnects. I have come to leave the BT Preferences Pane open all the time on my secondary monitor and I can see that Bluetooth turns off, then turns back on in about 5 seconds. Sometimes my MM automatically reconnects and sometimes I have to get out the RF mouse and toggle BT off and on. Usually this works but occasionally I have to do this a couple of times.
I don't run Android File Transfer any more -- it never ever worked for me -- and my Android phone is a secondary phone mostly used to test Apps so I don't really miss it. I do have a Satechi powered USB 3 hub that I've had for years. I don't think it is interference as bluetooth literally turns itself off.
So it is barely tolerable for now. I've started to make sure that software I buy can have the license changed to Windows. I don't plan to switch anytime soon but I want to keep my options open. Windows has gotten better and Apple has gone so far downhill and doesn't seem to be getting any better -- if this keeps up I figure they will probably cross next time I need a desktop.