When you click on the "+ Create a group" button you are presented with a pop-up. The pop-up has a note that says:
Note: specific devices can't be added to dynamic groups. Learn more about static vs dynamic groups (this last sentence is a link)
It see two problems with this:
1. What does the first sentence mean?
2. The second sentence which is a link, only gets you to https://staging.hosted.mender.io/ui/#/help. Which does not contain any information about static vs dynamic groups. and just left me even more confused then before I clicked it.