'Empty or invalid response \'\' for website id 1, Time elapsed: 1.941s, skipping'
in this case WP nggallery started an ob_start() handler causing the archive output to not appear on CLI. Other plugins might have caused this issue as well.
It would have been also fixed by launching climulti without the
-q parameter (
app/console climulti:request -q --matomo-domain...) but not sure what removing that parameter would break. Was initially added in https://github.com/matomo-org/matomo/commit/54be28167099a063228b5707c1857deac1248feb#diff-884529fcd1f2c23383c971d5c19372ab