Checking the VMNSDg_A log from %VCS_HOME%\Logs, would reveal below error
VCS WARNING V-16-10051-19538 VMNSDg:datadg:monitor:The DiskGroup is configured on disk (Signature:-XXXXXX, DiskBusType:9) that can be shared. Configure the SkipStorageValidation attribute to 1 for this resource or switch to use a clustered disk group (VMDg) for such configurations.
The resource type "VMNSDg" stands for "Volume Manager Non Shared Diskgroup" and is used in cases when there are plans to use non-shared storage in Cluster.
The SkipStorageValidation attribute needs to be enabled to support external disk or disks that are configured on the same SCSI controller as that of the OS disk
For more information, please refer https://www.veritas.com/support/en_US/doc/129406946-129406949-0/br731_wxrt-tot_v75450513-129406949
1. Highlight the VMNSDg without expanding the tree. On the right pane, top right, click on "Show all attributes"
2. Select SkipStorageValidation attribute and select Edit.
3. Enable checkbox on SkipStorageVailidation as seen below

4. Once done, "Save and Close Configuration" from Java Console, to save the changes.
CAUTION: "SkipStorageValidation" attribute should only be used, when it is known for sure that the disks are not shared across nodes. Possible data corruption may occur if the attribute is enabled for shared disks