Ah, figured it out. It's due to a really bad connection. There's a spinner with white background. The underlying page loads (I can see parts of it if quickly scrolling), but the spinner div won't go away. Minor issue that wouldn't affect most of your visitors.

Print: https://imgur.com/UqSUUTA

On a faster connection it worked fine. Not sure what this spinner is (can't debug on mobile). Ordinarily I wouldn't bother much making my service accessible for those with extremely crappy connection, but given your service might be used by people on 3rd world countries, behind proxies and so on, it might be a good idea to simulate slow connections on your landing page :) Maybe adding a "close" button would solve

Ubuntu 16.04 LTS stands for Long Term Support, so it stays supported longer than non-LTS versions. Software can be out of date, but its rock solid. Instead of updating software (like on Windows and macOS) they backport security & reliability fixes from upstream.

Some people also don't wanna run 57 (yet) because their favourite extension(s) aren't ported from <= 56 yet. So they stay on older versions. Current ESR (Extended Release, akin to LTS) is 52.