We are using MongoDB to store some historical data and occasionally insert performance degrades drastically (up to hour for one record) or hangs.
Issue was reproduced few times on MongoDB 3.0.1 and 3.0.6.
Symptoms are the following:

• inserts are slow or hang
• mogostat hangs
• mongotop works and shows 0 numbers
• remote Robomongo hangs on attempt to connect
• local mongo shell connects and can perform some commands but hanging on getting db/collection stats and queries

pstack, WiredTiger stats, parts of mongod log, biggest DB stats and few longest Operations are attached.
Some data removed as it can be sensitive.