Maybe everyone already knew this

Maybe everyone already knew this - but maybe not.

Be really careful that you don’t have multiple Arduino XOD projects plugged in to various USB ports at once… as you are trying to upload new sketches.

It sounds obvious that there would be issues that would be immediately able to be recognised, but that isn’t actually the case. For example, I had part of the sketch working - but other parts not - when I uploaded in debug mode. (What works depends on what hardware the other board had wired into place!)

I just couldn’t figure out what was going on - until I happened to look up and see the other project happily working (a room thermometer) that I had permanently plugged in.