slider causing website to be not Mobile friendly

I go to this URL to test my site:
https://www.google.ca/webmasters/tools/mobile-friendly/

Sometimes my site is Mobile friendly sometimes its not. When I change in Appearance settings, the option for the Slider:

Full width slider

When checked, the front page slider occupies the full viewport’s width

I leave it unchecked normally. Then if I check it, save it, the website remains NOT mobile friendly.
But if I check it, save it, uncheck it, save it, then the website becomes mobile friendly.

This fix only works sometimes. Other times it does not work.

please help me figure out why this setting may be affecting the google mobile website test.