appointments+ calendar / reservation page not showing correctly

I have troubles rendering the calendar/reservation page correctly to non logged in users: the problem being, oddly enough, that the page doesn't show at all the appointments+ section but it displays the share buttons twice.
I tried disabling the share buttons plugin, but the problem is not solved:
instead of the appointments+ section, the share buttons are shown only once(in kind of default mode graphics and even if the plugin is not active).

the problem doesn't seem related to the device used, but rather from the fact that I was logged in as administrator (or editor) or not.
The problem described happens if the user is not logged in (eg. the appointments+ section is not rendered and the share buttons are shown twice)

If I am logged in as administrator (or even editor) the page is displayed correctly.

The problem keeps happening if the user is not logged in:
I tried with twenty fourteen: same problem
I tried disabling "google analyticator", "White Label CMS" and even "ithemes security" which are the only plugin I can think of messing around with the code. nothing changes.

Plugin versions:
Simple Share Buttons Adder v4.3
Appointments+ v1.4.3.1