Thank you for your message, I have been investigating the issue describe and also discovered that some files when corrupted or deleted from the Local Library are not downloaded again. This issue has been reported to the development team who will investigate and resolve this in a later release of the Xibo for Linux Player. Thank you for posting about this on the forum and making us aware of the issue.
In the meantime, a workaround would be to delete the
cacheFile.xml file from the directory
~/snap/xibo-player/common directory. Mine was located in the latter directory and I found that after deleting this file, the Player successfully downloaded the files missing from the Library.