This has been happening to me for around 2 months now, with every update I hope this is fixed but no luck
Currently using:
Version:63.0.3368.88
Opera is up to date
Update stream:Stable
System:Mac OS X 10.13.6 64-bit
I have un installed, re installed, created new accounts, disabled extension, cleared caches and nothing seems to work.
I love this browser but its getting to that point now.