Previously we were running Mongo 2.4.10 in our production environment. Last night I upgraded it to Mongo 2.6.12 as our plan is to eventually upgrade to 3.4 so we can migrate to Atlas from being self-hosted. Since upgrading to 2.6 we've been seeing very high CPU usage (200% pretty consistently) on the server (replicaset of 1 primary + an aribter). mongostat isn't reporting anything out of the ordinary, so I tried running mongotop to try and diagnose the problem, but I'm getting:

assertion: 13106 nextSafe(): { $err: "BSONObj size: 67108859 (0x3FFFFFB) is invalid. Size must be between 0 and 16793600(16MB)", code: 10334 }

If I go into the mongo shell and try:

rs0:PRIMARY> db.adminCommand("top");

I get:

2017-01-07T18:36:34.039+0000 error: {
    "$err" : "BSONObj size: 67108859 (0x3FFFFFB) is invalid. Size must be between 0 and 16793600(16MB)",
    "code" : 10334
} at src/mongo/shell/query.js:131

How can I fix this issue? More importantly, how can I address the high cpu usage.