Is using the Magic Mouse 2 & original Magic Mouse on the same Mac unsupported in High Sierra? I recently upgraded my mid 2011 Mac mini to macOS High Sierra. I purchased the Magic Mouse 2 about a year ago, but really loathe the charging port on the bottom (unbelievably stupid design, but I digress). As such, I kept my old (original) Magic Mouse handy for when I needed to charge the Magic Mouse 2. I never had problems with this use case in OS X El Capitan. 

However, today when I tried to use the old Magic Mouse, macOS absolutely freaked out and neither of the Bluetooth mice could connect. I had to use a generic Logitech USB mouse to "forget" both of them (old and new), then I could reconnect the Magic Mouse 2 after it charged. 

So my question: is the original Magic Mouse unsupported in macOS High Sierra? (edit: it definitely is supported, not the issue). Or perhaps I simply can no longer use the Magic Mouse and Magic Mouse 2 interchangeably? 

Update 1: Forgetting and re-pairing both of the the mice was a temporary fix. Nothing else worked, including rebooting. 

Update 2: Issue has returned. I again had to fight macOS tooth-and-nail to get the Magic Mouse 2 paired after using the Magic Mouse!

Update 3: One thing I forgot to mention: when the Magic Mouse 2 has lost pairing (after using the Magic Mouse) and I plug it in and switch it on, the "Mouse" section of System Preferences goes absolutely berserk, rapidly alternating between the normal screen and the "looking for bluetooth mouse" screen.
I cannot find any Apple documentation stating that the original Magic Mouse is unsupported in newer OS versions. 

Your problem is more likely to be just one of Bluetooth connectivity. Apple provides a troubleshooting document that describes the Magic Mouse and Magic Mouse 2 together. Other remedies for problems can be found here.

The Magic Mouse is not one of Apple's strongest designs, and you may prefer a third-party mouse, or the Magic Trackpad, which I find much better. (You can leave it plugged in while using it, for starters!)