When clicking the update icon in the menu bar nothing apparently happens but LibreOffice then no longer responds to any input.
Check for updates from the help menu does not fail, but shows no updates (correct as I am using the latest release version).
However, if you open the extension manager and check for updates there, LibreOffice does hang, consuming >100% CPU. So it looks like the problem is with the extension manager.
*** This bug has been marked as a duplicate of bug 99784 ***