Description.
The conflict can be, if the theme is using Bootstrap library and version of Bootstrap is different then version in Booking Calendar. Booking Calendar is use bootstrap library 3.3.5

Such conflict can make issue of opening and immediate closing some interface elements (like drop down lists or modal windows), or issue with showing tooltips or popovers, etc...

How to fix?

1) You can open the Booking > Settings General page and in Advanced section click on " Show advanced settings of JavaScript loading " link and then set as checked only this option " Disable Bootstrap loading on Front-End ".

Then Save the changes and test it.

Please note, in this case, possible issues with not showing mouse over tooltips at the front-ens side in Booking Calendar. Its tooltips for showing booking data, times and cost, when mouse over specific day.

2) Other solution can be to load CSS and JavaScript files of Booking Calendar only at the page(s) with booking form or availability calendar and do not load such files at all other pages. If you want to make such fix, then open the Booking > Settings General page and in Advanced section click on “+ Show advanced settings of JavaScript loading” link. Then set as checked this option “Load JS and CSS files only on specific pages” and in textarea specify all relative urls of pages with booking forms. One url per one line, like this:

/booking/app1/
/other/service1/