I've tried this in three different Device folders. Two related to the UniFiAP plugin, and in the DEVICES non-folder.
If I select all (which is the only way to get a count of the devices aside from doing it manually) the Indigo client hangs with a beach ball. Not sure if this ever ends, but it lasts at least 30 seconds and that was the end of my patience before force quitting the client.
Doesn't happen in other folders not related to Devices.