Usually this happens when your browser and the server do not agree about that group of units.

It may be because you are having lag in the connection with the server, indicated by the spinning arrows in the lower right corner. If you hold your mouse over it you should see "server state connected" show up if it is good. Click it to refresh.




Next thing to try if clicking that connection button does not fix your issue is to close the browser tab and reopen it. This will solve the problem 98% of the time


In perhaps 1% of the cases you will need to clear the cache from your browser and restart the browser, because your browser is arguing with the server about the location of the units, and the server is rather headstrong about it being in charge and not listening to your browser. I have found very few cases of this using Chrome, while other browsers have not been as good.




If the problem persists after clearing your cache and restarting your browser you can submit a bug report, and mention that you tried to resolve the issue already by doing the above steps.