I’m having the exact same issue. My site is still under construction and not launched. I have updated my static front page, but when I try to view it, the updates are not there. The only way that I can see my changes is if I check the box in the customize menu (under static front page) that says “keep the old static template?”. I then can see my updated changes that I published to the homepage, however I lose my big title section slider as soon as I do this.
I have made changes to my static front page in the past without a problem, which makes me think that there is a problem with the theme and not with the settings I have chosen. This is very frustrating.