This is from the coverage step of the workflow on a PR: https://coveralls.io/builds/67179524
This is the overall result you get if you click on a coverage badge: https://coveralls.io/builds/67179061

Note that objective_c_tests is missing from the Subprojects list, and if you expand the source tree, pkgs/objective_c/lib/src/ns_data.dart is uncovered. Seems that coveralls is just dropping the objective_c subproject.