3D FlipBook - 3D flipbook not working under WP 5.3

Hi, we have 100 flip books installed on our website.. and all worked perfect but now they do not show up anymore on the WP frontend. We can work with the backend, generate the shortcakes and post them in postings and pages.. but in the frontend no flip book can be seen.

Examples:

https://wilderness-society.org/european-wilderness-publications/european-wilderness-quality-standard-audit-report-uholka-shyrokyy-luh-wilderness/

https://wilderness-society.org/european-wilderness-publications/european-wilderness-society-corporate-design/

We can see the flip books in the frontend if we are logged in the backend on Mac Safari.. But in. fresh google chrome browser and other browsers where we are not logged into the backend, the flip books just do not show up.. Please fix this ASAP