node-mongodb(replica set) memory issue ( error : no primary found in replicaset + electionTimeout )

Problem:

Twice or thrice a day our node-js process memory goes high and restarted or errored. ( normally it's fine with read & write operation ). I'm getting the following errors when this happened.

1. [MongoError: no primary found in replicaset] www-1 name: 'MongoError', www-1 message: 'no primary found in replicaset' }

2. pm2 request timeout about 10 sec > I think it's related with electionTimeout ( https://docs.mongodb.com/manual/reference/replica-configuration/#rsconf.settings.electionTimeoutMillis )

Configuration:

MongoDB 3.2.4 replica set with 3 server (m4.xlarge)

Nodejs using pm2 4 cluseter x 4server (m4.xlarge)

rs.conf setting:

"members" : [
{
    "_id" : NumberInt(0), 
    "host" : "host1:27017", 
    "arbiterOnly" : false, 
    "buildIndexes" : true, 
    "hidden" : false, 
    "priority" : NumberInt(1), 
    "tags" : {

    }, 
    "slaveDelay" : NumberLong(0), 
    "votes" : NumberInt(1)
}, 
{
    "_id" : NumberInt(1), 
    "host" : "host2:27017", 
    "arbiterOnly" : false, 
    "buildIndexes" : true, 
    "hidden" : false, 
    "priority" : NumberInt(1), 
    "tags" : {

    }, 
    "slaveDelay" : NumberLong(0), 
    "votes" : NumberInt(1)
}, 
{
    "_id" : NumberInt(2), 
    "host" : "host3:27017", 
    "arbiterOnly" : false, 
    "buildIndexes" : true, 
    "hidden" : false, 
    "priority" : NumberInt(1), 
    "tags" : {

    }, 
    "slaveDelay" : NumberLong(0), 
    "votes" : NumberInt(1)
}]

"settings" : {
"chainingAllowed" : true, 
"heartbeatIntervalMillis" : NumberInt(2000), 
"heartbeatTimeoutSecs" : NumberInt(10), 
"electionTimeoutMillis" : NumberInt(10000), 
"getLastErrorModes" : {

}, 
"getLastErrorDefaults" : {
    "w" : NumberInt(1), 
    "wtimeout" : NumberInt(0)
}, 
"replicaSetId" : ObjectId("577de60fc5cb2c022f96841f")}

Question:

1.Why am I getting this error?

2.Does MongoDB replica set election occur even if each server has a good health?

I'm not sure if I understand this document correctly. https://docs.mongodb.com/manual/replication/#asynchronous-replication

3.What if I set MongoDB electionTimeoutMillis lower than 10sec. Does this help?