Bookmark doesn't work

I have recently developed a course in Storyline in Classic Player that worked perfectly when publishing to LMS. Last week I had to update the course by removing one slide. When publishing the course again in the exact same way as before (Completed/Incomplete), the bookmark suddenly doesn't work: On the pop-up window that asks if I want to continue where I left, the 2 buttons Yes and No are unable to press and a the "hourglass" icon spins endlessly. I have made all recent updates to Storyline. Is this a bug, does anybode experienced the same problem, and/or is there anything I need to do differently? Thanks a lot.