After upgrading to 9.10 only one of my three ESXI hosts is able to mount my ISCSI drives. Rebooting off of my 9.3 installation restores everything to working condition.
Please create a bug report at bugs.freenas.org and post the issue number here. In the bug report, include a debug which can be created using System -> Advanced -> Save Debug.
Just to add I am seeing the same behaviour. 9.3 on the same box works on 3 hosts, 9.10 works on one host, the others see the iscsi volumes as snapshots and refuse to use them.