3D FlipBook - Stuck at processing... and can't access settings

Hi, we currently face an issue where it says on all our flipbooks "Please wait! The book is processing...". Additionally we have the issue that we can not access "Book properties", "Sheet properties", etc. - they are all grayed out and disabled. Console shows following error: Unhandled Promise Rejection: TypeError: undefined is not an object (evaluating 'PDFJS.GlobalWorkerOptions'). We updated the plugin from I believe Version 1.16.13/14 to Version 1.16.16 but didn't solve the issue. (Lifetime License".