After a range is deleted, the collection lock is released and there is a wait for the deletion to become majority committed. Such wait is synchronous in 4.2 and asynchronous in 4.4.

As a side effect, a range deletion task can be scheduled right after the previous one causing long unavailability of the collection for any operation due to this lock being continuously acquired by the range-deleter thread.

While r/w/chunk operations and transactions can timeout waiting for the for the lock, there is no such constraint for the range-deleter and this makes it even more probable for it to get the precedence.