From the referred URL: "A calendar bug fix (MDL-67494) released with Moodle 3.9.5 and 3.10.2 unintentionally corrupted some calendar events during the upgrade process. We have reverted MDL-67494 and have now released Moodle 3.9.6 and 3.10.3 which is the version you should upgrade to (skipping 3.9.5 and 3.10.2 if possible)." Reproducible: Always
This bug has been closed with the following commit: https://gitweb.gentoo.org/repo/gentoo.git/commit/www-apps/moodle?id=9c56302174a41ed09235a77740ab0fafbbd82ad7