We were having an issue with Appointments + . The site was displaying an error when looking at the calendar availability your agent thought it may have been plugin compatibility related.
I have just gone through and found what was triggering it.
basically on the page that displayed the appointments, it has there shortcodes...
[app_pagination step="2" month="1"]
If I removed the one that has [app_monthly_schedule add="1"] then the page worked fine, but if I added it back in, it crashed.