I made a change on our NEL/Reporting API report collector earlier which changed the response status from 500 to 403 when the client fails to send a valid/any Origin request header on the POST.
This caused a ~2x increase in reports.
(ignore the spikes, they're known)
I then changed the response from 403 to 201 and the reports returned to their previous level. No other changes were made.
Anyone know why this'd be? Would browsers retry on 403?