I found that section-templates. such as Expand section, don't show on mobile.
I can see the note neither on the mobile version of Wikipedia nor the mobile app. Article hatnotes seemed to always show fine - for them it says "Page issues" (which can be shown/expanded by a click on it) - hence for sections it should say "Section issues". Redrose64 said that this would be due to Module:Message box using the metadata class, which is "always hidden in mobile".
Whatever the issue is here - please fix it ASAP! Mobile users should also be able to see section-templates, it probably means that there needs to be an alternative way for doing whatever the metadata class was hidden for - however an exception or alike might work as well.