This was triggered by the stackoverflow question at https://stackoverflow.com/questions/68847579/how-to-make-a-browse-request-to-the-musicbrainz-api-with-the-offset-and-limit-ar.

https://musicbrainz.org/ws/2/release?artist=9c9f1380-2516-4fc9-a3e6-f9f61941d090&inc=recordings&limit=100&fmt=json says there are 435 releases for the artist (""release-count":435"), so without any offset and a limit of 100, one would expect to find 100 releases in the response. However, there are only 85. Playing around with a few offsets (but always keeping offset + limit under 435), I always get an arbitrary not-equal-to-100 amount of releases in the response.

As soon as I remove inc=recordings, or replace it with release-groups+ratings from the SO question, the responses are OK.

This applies to both the XML and JSON web services.