This thread is resolved. Here is a description of the problem and solution.
The update from within WP Dashboard (or by uploading the .zip Plugin folder) produces this error : PCLZIP_ERR_BAD_FORMAT (-10) : Unable to find End of Central Dir Record signature
Solution: Please review this 2 threads: https://wpml.org/it/forums/topic/problem-to-upgrade-the-plugins/
The issue is sporadically happening and can be solved (usually) by a manual update / install of the plugin
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