I have an app on Heroku and Mongolab. I use node.js and mongoose. Heroku often logs that my memory consumption is over their limit and part of it is swapped to hard-drive. From time to time I have disconnected from my Mongolab database, so my entire app is down for about 5 minutes. At the beginning I have couple of Heroku timeouts. After that, Heroku restart my app and I have Error: failed to connect to [ds057900.mongolab.com:57900] multiple times. After couple of restarts it backs up. Mongolab team tells me that on their side is everything ok. Heroku team tells me that it may be memory issue. One full restart isn't enough to up my app back. May it be a problem with memory leaks in my app?
Seems like you are using Heroku's add on for mongo DB, give a try to any database of you own rented by Mongolab or MongoHQ.