I am using PHARMACY theme which is a child of STOREFRONT. When I use a mini-calendar view of an Event CALENDAR it looks unintelligible on a mobile device. Event calendar is a responsive plug-in. Instead of a shrunk down version of the desktop view it stacks dates in an unintelligible manner. It works fine in the "Twenty-Six" theme (which I tested. I also have had similar problems with plugin Tables. I've had to scrap the tables completely and are having my Full Calendar unseen by mobile devices.
If it's working properly on one theme, but not on another, I'd suggest reaching out to the developer of the theme to have them take a look at how it's being implemented. They may be able to offer you a workaround, or simply make an update that will allow it to function as intended. Good luck!