The count is shown as "380 144 960" in the "Export query" and "Select Export File Type" dialogs.

To reproduce:

pick a collection
run a query that only selects a portion of it
export with filter
pick JSON (or CSV)
look at the document count in the progress indicator part of the export dialog: Trying to reproduce count of "380 144 960".

Still trying to repro and collect customer details. I tried to repro with collection with 2 million documents, but query filter export has been working ok.

May be similar to https://jira.mongodb.org/browse/COMPASS-4255