As of February 2018 this issue is happening with a newly downloaded fresh copy of Opera 50.0.2762.67 on Mac OS X 10.13.3 64-bit.
Features of the extensions that work when browsing do work. However other features available from the icons are not because the icons do not work.
I have the following extensions installed:
LastPass
RainDrop
Grammarly
Office Onine
OneNote
Any help welcome
Thanks