Yesterday I upgraded my Mac to Sierra (the most recent OSX release and required in order to update to XCode 8) and discovered that Karabiner (a key mapping program) doesn't work with Sierra. I use Karabiner on the Mac and AutoHotKey on Windows to map my keys so that both Mac and Windows are the same, since I use both OS's about equally.
Today I used git to merge in changes from the online repository and XCode 8 lost track of all the project files. It now believes the project is empty, even though Finder sees the files. XCode 7 didn't have this problem.
The day before yesterday the router decided to go crazy and wouldn't let me network between my Mac and Windows machines for more than a few minutes. I had to keep reconnecting. Power cycling the router didn't help. The problem went away by itself.
What will it be today? Who knows, but it will be something. At some point maybe I'll write some code.