Thanks for clarifying that.
After experimenting with HTTPS testing on my mobile with the multi-threaded test, I was able to replicate a similar test result by turning on "Data Saver" in the Android Chrome browser.
Data Saver - Left: Off, Right: On
As far as I can tell, the Data Saver strips comment tags from webpages, so in turn strips all the random test data. So maybe an idea to test if Data Saver is on is to have something like a piece of JavaScript check if a certain HTML comment tag is present in the page source. If it's missing, display an error message saying to disable Data Saver.