I know it's an old board, but it did used to work. Today I got it out to try and load a new program on it. Here's what happened.
The IDE cannot even detect it on Mac (IOS system information can see it, though), even after I install the proper drivers.
On PC, I can connect it, I can see the onboard memory in Explorer, and when I open the IDE, I can select the proper port and the IDE detects what it is right away. When I select the board, it shows up in the lower-right corner saying, "ItsyBitsy M0 connected on COM4 (or 6 or whatever)".
Then, if I try and upload even the BareMinimum sketch, nearly every time it will deliver an error and say "No device found" on the port. Even though, most of the time, it will STILL say in the bottom-right corner that the board is connected to that port.
After resetting the board, double-clicking reset, connecting and disconnecting, reloading the IDE, doing all these things in every order, at some point a sketch FINALLY uploaded. But now I can't figure out what went right that time. I can't replicate it.
Could this be caused by a power problem on the USB bus? That wouldn't explain why I can't seem to get it to work on my Mac, though (though that could be an unrelated problem).