The WiredTiger storage engine has a default journal log file size of 100MB, so for every 100MB of data written to the journal a new journal log file is created.
A race condition in the WiredTiger code when switching to the next journal log file may cause some updates to be lost during an unclean shutdown.
This issue only affects users running with journaling enabled. Users that run with journaling disabled can not be affected by this bug.
If the race condition is triggered and the node suffers an unclean shutdown, some updates since the last checkpoint may be lost. Unfortunately it is not possible to detect if the race condition has been triggered.
Only MongoDB versions 3.2.6 and 3.2.7 are affected by this bug.
A fix for this issue is included in the MongoDB 3.2.8 production release. Users running 3.2.6 or 3.2.7 whose nodes may be subject to unclean shutdowns should upgrade to MongoDB 3.2.8 to avoid exposure to this issue.
Unfortunately there are no known workarounds for this issue.