We did exactly same upgrade from 6.2.2 to 6.2.6 with ISSU; just make sure you don’t have any
aclmgr inactive configurations so before ISSU run these two commands on each VDC
sh run aclmgr inactive-if-config
clear inactive-config acl
Also I had one failed upgrade on my first try due MST changes so try to make this when n the network is more quite
Hope it helps