Thank you. I have update the add-in to version 1.4 now (de-installation, shut down, installation, started arcgis pro again). This seems to be the same problem as before and I can not detect any changes, as nothing becomes visible clicking the icon: none of the expected sub-windows becomes visible, clicking on the most left icon "i" has the same effect: nothing. Any icon becomes a grey colored one after an extremely short visible spinning wheel, that's it. Afterwards you can not click it again.I have checked light and dark layout. There is no vpn running. I have installed all patches currently available for ArcGIS Pro 2.2. No other add-in is loaded.
I will be able to install ArcGIS Pro Version 2.3 next week and try again.