Probably a dumb question, but have you tried clearing the browser cache and making sure cookies and Javascript are enabled?
Also, if you're running Little Snitch or similar software, try stopping the filter; it's possible something critical's being blocked. I've seen tabs and checkboxes go missing on forums due to LS, for example.
Not that you would know, but I work in the I.T. hardware and software side of life. That doesn’t necessarily mean I have all the answers. I did blow out the cache and tried Chrome. I also ran it from a Windows 10 machine, my iPad Pro and also 2 other Macs and still no lift-off.