mongodb configuration: 2shards, 3instances each, 3 config servers, remote mongos, 52mbit network between mongos and mongod, 1gbit between mongod's

I'm trying to retrieve data from mongodb via single .find() query in mongo console.
code:
var i=0;
var cursor=db.load.find();
while(cursor.hasNext())

{cursor.next();i++;}

;print;

while attempts to do so on the local machine are always successful, the query on remote mongos fails repeatable on the same entity.
entities length seems to be homogeneous.

console output:
1670457
getMore: cursor didn't exist on server, possible restart or timeout?

db.load.count():
3236686

db.stats():

mongos> db.stats(1024*1024);
{
"raw" : {
"rset01/load1ft:27017,load2ft:27017,load3ft:27017" :

{ "db" : "test", "collections" : 4, "objects" : 1670511, "avgObjSize" : 5729.003803027936, "dataSize" : 9127, "storageSize" : 9734, "numExtents" : 40, "indexes" : 4, "indexSize" : 376, "fileSize" : 16313, "nsSizeMB" : 16, "ok" : 1 }

,
"rset02/load1gt:27017,load2gt:27017,load3gt:27017" :

{ "db" : "test", "collections" : 3, "objects" : 1566193, "avgObjSize" : 5903.711271854746, "dataSize" : 8818, "storageSize" : 9223, "numExtents" : 39, "indexes" : 2, "indexSize" : 348, "fileSize" : 14266, "nsSizeMB" : 16, "ok" : 1 }

},
"objects" : 3236704,
"avgObjSize" : 0.005544220293236576,
"dataSize" : 17945,
"storageSize" : 18957,
"numExtents" : 79,
"indexes" : 6,
"indexSize" : 724,
"fileSize" : 30579,
"ok" : 1
}

mongos logs:

Mon Aug 27 18:49:16 [conn1] want cursor : 1975918310978336011
Mon Aug 27 18:49:16 [conn1] CursorCache::get id: 1975918310978336011
Mon Aug 27 18:49:16 [conn1] scoped connection to load1ft:27017 not being returned to the pool
Mon Aug 27 18:49:16 [conn1] AssertionException while processing op type : 2005 to : testing.load :: caused by :: 13127 getMore: cursor didn't exist on server, possible restart or timeout?