EXOS switches prior to 16.2 are vulnerable to a kernel deadlock due to the leap second, if NTP is enabled. SNTP is not affected. NTP advertises the leap second for 24 hours prior to the leap second occurring, so the workaround is to disable NTP at least 24 hours before the leap second.
EXOS 16.2 and EXOS 21.1 are not affected by this. Please see the following GTAC Knowledge article for further information:-