Course Presentation

There is a problem with two H5P Course Presentations:
The user opens the the page and there is no H5P content displayed but a grey line. All other Course Presentations work well.
Unfortunately it is not clear since when the problem exist. Propably it was first detected in January but we do not check all our H5P contents regularly.

Platform: WordPress 4.9.5

Browser: Firefox 57.0.2 and Safari (both Mobile and Desktop)

H5P plugin version 1.10.1

H5P content type and version:
Course Presentation (1.17.9)

Do you have any idea why I'd get an "invalid security token" (cf. screenshot) when trying to load an .mp3 into the Course Presentation tool?

English Park: For beginner-level English language learners.

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