Customizer has error – warning, live view and preview differ

I have a MultiSite.
BuddyPress is active on one subsite. I chose Custom Community theme for it.
No issues with other themes
I have deleted and re-installed Custom Community with no changes in the issues.

When I open the Customizer with Custom Community, I get a warning:

Warning: Creating default object from empty value in /home/toniengl/public_html/wp-content/themes/custom-community/includes/admin/customizer-options.class.php on line 578

1). The live site and Customizer preview look very different from each other:
– the site name font is very different
– the layout below the header is different
– no slideshow on the live site
(but maybe the theme default slider does not appear on the live site?)

2). In the Customizer, when I hit “Save & Publish” the button does not change to “Saved”, but some changes are saved

https://toni-esl.com/eslbuddy/

I need to put a working theme back in place for now. I can change it whenever anyone needs me to do so for troubleshooting.

Thank you