In 15 years I've never had any of those problems with Smugmug. And my rate was "grandfathered in" 15 years ago so I paid only $30/year for the first 12 years. It's now $47.88/year with unlimited uploads.I have used Zenfolio since 2007. Nothing professional of course.
In the last years, I find the response times are really, really bad. Frequent interruptions and page freezing.
Images not loading, pages not loading, taking forever before uploaded images become available, linked images in posts disappearing from time to time, etc.
Changes in behaviour of page options they won't even admit.
If I hadn't that many images stored, I would have left a long time ago. It will probably be one of my first projects for when I'm retired. Unless the issues are fixed by then - "their engineers are always working hard and monitoring the system performance to get the issues fixed". So, who knows...
I most certainly wouldn't recommend Zenfolio to anybody starting now.
It is relatively cheap though, 40USD for a year, unlimited storage.