Stop Customizr from automatically stripping HTML of classes

Hello!

I recently switched my theme to Customizr. Immediately a plugin I depend on stopped working. After contacting the plugin developer, she informed me that the functions that weren’t working correctly were due to the theme stripping all HTML of classes, which led to the plugin not being able to position the images correctly.

Here are the main problems I’m experiencing:
1. The book cover won’t switch sides when I attempt to do so in the UBB settings, despite “updating successfully”.
2. Only the book title and author appear next to the book cover whilst the rest of the info only appears below the cover.
3. The book cover appears after the Dropcap, breaking the first sentence (or word) apart.

The Plugin I am using is the “Ultimate Book Blogger” plugin.
You can find an example post here: https://wp.me/p4Ag7r-17D

Thank you in advance!

Best,
Karolina