Customer Support Bulletin CSB-190819-1 / -2

Description:

FortiGate units running in HA with uninterruptible upgrade enabled may fail to synchronize upon upgrading to FortiOS version 5.6.10, 6.0.6, or 6.2.1. The issue is related to the time taken to synchronize data and sessions between the primary and secondary HA units and is observed more readily with larger configurations.

for full information see the support portal

anyone who had an issue with this while upgrading to 5.6.10 / 6.0.6 / 6.2.1?

i find the text a bit unclear, they first mention it is only relevant for upgrade to these versions and then advise to the disable uninterruptable upgrade for upgrade from these version.