After network fluctuation disk group is imported on both nodes

Do you have fencing configured? Do you have SCSi-3 complaint disks?  Fencing prevents such issues from occuring and prevents data corruption.

If no fencing is configured than during network partitions each node in the sub-cluster thinks that the other nodes in the cluster is lost and it will try to bring the service group online.

You may have faced similar problems.

Read more at https://www.veritas.com/community/articles/symantec-cluster-server-io-fencing-architecture-guide

You engine log is not attached.

Regards,

Sudhir