mongodb find query getmore operation hangs - mongodb

Question

We are running MongoDB 3.0.2 on Linux.
The "getmore" operation for a find query periodically hangs.
The operation is available currentOp(), and one item I cannot explain is that all the acquireCount values in lockStats continue to grow while the query hangs (for Global, MMAPV1Journal, Database, and Collection).
This is the operation in question, at this point running for more than 1000 secs, returned by db.currentOp() :
{
"desc" : "conn60",
"threadId" : "0x2a99ee0",
"connectionId" : 60,
"opid" : 67792,
"active" : true,
"secs_running" : 1098,
"microsecs_running" : NumberLong(1098289543),
"op" : "getmore",
"ns" : "dbName.collectionName",
"query" : {
"d" : {
"$gt" : ISODate("2016-03-13T18:00:00.261Z"),
"$lt" : ISODate("2016-03-14T22:45:17.718Z")
},
"cc" : "US",
"dc" : {
"$in" : [
"26",
"31",
"17",
"29",
"35"
]
},
"pr" : {
"$gte" : 4
}
},
"client" : "10.0.0.111:33670",
"numYields" : 317557,
"locks" : {
},
"waitingForLock" : false,
"lockStats" : {
"Global" : {
"acquireCount" : {
"r" : NumberLong(635114)
}
},
"MMAPV1Journal" : {
"acquireCount" : {
"r" : NumberLong(317557)
}
},
"Database" : {
"acquireCount" : {
"r" : NumberLong(317557)
}
},
"Collection" : {
"acquireCount" : {
"R" : NumberLong(317557)
}
}
}
}
Any insights would be much appreciated ! Thank you in advance.