So, just to post an update. It appears there was a misunderstanding, or that this wasn't explained properly.
I had assumed, that preventing F5 from working on Speed Dial didn't have any requirements. I had understood it to mean that none of the speed dials would refresh. And that is why I thought this wasn't working and that there was some sort of missing flag or option I needed to enable.
However, once I grabbed some favicons and replaced the thumbnails with those favicons, that was when the F5 stopped refreshing those speed dials. It appears that you are required to use a custom thumbnail in order to prevent F5 from updating that speed dial.
The one speed dial option that I didn't customize will still refresh when F5 was pressed. But all others do not change the thumbnail assigned to them. It stays the same and no longer replaces the speed dial with a screenshot of the website.
The reason why I mentioned this was that I thought I needed to recreate my profile from scratch. But that isn't the case. I just wish it was a lot more clear that you have to select a custom thumbnail in order to prevent the F5 button from working.
I hate this new update to the Vivaldi website where the top menu pops in and out as we scroll up and down the page. Popping menus on websites are super annoying and degrades usability. Please get rid of it, and return to a simple predictable static top menu, so we can scroll up and down the page without the popping annoyances.
[bug reported VIV-1282]