I have the same problem on FT and had wondered if it was the result of browsing on my four-year-old Mac, but even after replacing it with a brand-new 2018 Mac Mini, I still routinely see the spinning pinwheel, my FT tab freezes, and Activity Monitor reports that FT is using over 100% of my CPU's power.
This is literally the only time my new CPU is taxed -- not to mention the only website doing it.
I realize you've reported it, and I don't mean to pile on, but something is seriously amiss with your site code and/or ad configuration.