Unfortunately, there's no way to change the read-only mode back to normal and resolve the issue. Repository folders with data and metadata can be copied over to some temporary storage.
iSCSI LUN need to be deleted and recreated using normal provisioning mode.
Then repository can be copied back to it.
It's possible that iSCSI initiator on the Core need to be removed and recreated to the new iSCSI LUN. Then repository needs to be re-attached to the Core.
