It happens on both previous and current version (188.8.131.52_20180530).
The error alert is always the same:
I'm on Win7x64, Office 365 Business, Excel Version 1805 (Build 9330.2087)
On trying to add connectors manually, putting i.e. GooglePlaces.xml into /connectors/ folder i fail too - added connector doesn't appear in any ribbon dropdown.