By default, the first VNIC port1 is enabled for jumbo frame. You must configure the same on the newly added VNIC port2. For jumbo frame support, refer to the following KB note.
If you look at the VNIC information in the CLI, MTU is set to 9000 by default.
After adding the second VNIC in the previous step, it is not set with the jumbo frame by default. As you can see, the MTU is set to 1500.
Run the following CLI commands to change the MTU size on port2. See Interface MTU packet size.
config system interface
set mtu-override enable
set mtu 9000
Check if the MTU changed as expected.