"pymongo.errors.CursorNotFound: Cursor not found" while updating Mongodb documents

Question

I am trying to update a collection in mongodb that has around 100k documents through the code written below. However after running for around 50k documents it gives below error

pymongo.errors.CursorNotFound: Cursor not found, cursor id: 632871094123

mapping_id_tree_old=[]
mapping_id_tree_new=[]
for i in range(0,len(resulttree)):
    resulttree1 = resulttree[i].values()[0:1]
    mapping_id_tree_old.append(resulttree1[0][1])
    mapping_id_tree_new.append(resulttree1[0][0])

dataNodeDictionary = dict(zip(mapping_id_old, mapping_id_new))
treeNodeDictionary = dict(zip(mapping_id_tree_old,mapping_id_tree_new))

it = treeNodeEmerald.find({"_id": {"$in": mapping_id_tree_new}})

for doc in it :

    if(doc.get('dataNodeId')):
        oldDataNodeObjectId = doc["dataNodeId"]
        if(dataNodeDictionary.get(ObjectId(oldDataNodeObjectId))):
            newDataNodeObjectId = dataNodeDictionary[ObjectId(oldDataNodeObjectId)]
            oldDataNodeObjectIdstr = str(oldDataNodeObjectId)
            newDataNodeObjectIdstr = str(newDataNodeObjectId)
            treeNodeEmerald.update({"dataNodeId": oldDataNodeObjectIdstr}, {"$set": {"dataNodeId": newDataNodeObjectIdstr}})