Recently upgraded to 2.1.4. This is the first new unknown device detected since the upgrade. One of the main reasons I upgraded previously to this version was for the feature to not get multiple email alerts on unacknowledged new unknown devices, which wasn't working in the previous versions. It appears this is now working in this version, except it locks up the program the second time it scans and finds the same new unacknowledged device. I do get the email alert the second time though.
For now, as a temporary solution, I have found I can restart the program and halt the scan before it gets to the new device, and thus before it freezes on a repeat of a new device. Then I can mark the device as 'known' (and put 'unknown' in the comment field since it's actually unknown to me) so it won't lock up during the alert.