Appointments's 'previous and next button' doesn't working

Hi, Dear WPMU.

I have another problem in using the Appointments.

The button(previous and next) doesn't working.

Here is address

I checked the file('class_app_shortcodes.php')'s line 647 as you explained at

The file is correct. But the button doesn't working now.

I tested with Divi Theme - v.2.3.1 and I will use with this theme.
I want't it working correctly.

Solve this problem plz ASAP

Thanks for your kindness.