We dropped a giant collection in a database. It certainly released the storage on the master but all the slaves still has the collection data file xxxxx.wt still lingering on the slaves. There is no replication lag and the logs on the secondary clearly show the drop did went thru the slaves.
2018-04-18T11:25:12.394-0500 I COMMAND [repl writer worker 7] CMD: drop < my big collection name here >

The version of MongoDB we are using is 3.2.19. Please advice.