The ocssd.log of surviving node shows a member kill request escalated to node kill request.
Cause: Starting 11.1, inability to evict a database or asm instance at the database level means that CRS gets involved and try to kill the problem instance. This is member kill request. If CRS cannot kill the problem instance, then CRS reboots the node because the member kill request is escalated to node kill request.
Solution: Find out the reason that asm or database instance could not get evicted at the database level (lmon, lmd, and lms initiated eviction). One common cause is that the instance was hanging and is not responding to the remote instance's request to die. Another cause is that one of more instance processes cannot be killed. One such example is that the process is in uninterruptible IO sleep.