A recent version of WiredTiger had changes to the log (journal) file format. Those changes are gated on a compatibility version being used by applications.

In order for MongoDB to start using the new log file formats, we need to connect the featureCompatibilityVersion mechanisms in to the WiredTiger compatibility configuration option.

There was a change included with the merge of WiredTiger that means MongoDB will currently only ever create V1 format journal files:
https://github.com/mongodb/mongo/blob/master/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp#L270