Log lines for slow operations normally list the collection on which the slow operation run.  There is one exception: for change stream operations, the log lists the original collection against which the change stream operation was run, even though the slow operation actually read from a different collection - the oplog (as all change stream operations do).

This can be a bit misleading, as the log line makes it look like the operation took a long time to run on the original data collection, even though it didn't run on that collection at all.

Ideally, the logged slow change operations should show both the original collection against which the change stream was run and the collection on which it actually run in practice (oplog).