I'm having this same issue. Just purchased a business plan, and anytime I select the "Colors" tab to play around with some new bg colors and font colors it just gets stuck on the spinning circle loading screen. I can edit the themes in the editor, but I can't apply them to the page. I can insert a video, or any other background image on the pages, I just can't load the "Colors" tab to play around with themes.
This isn't just happening with themes though, I just tried to adjust the colors of the mobile drop down menu, by clicking the colors tab on that set of edit options, and am also stuck on the spinning circle. Any ideas? Thanks so much!