The files for versions 2.2.0 and 2.2.1 have a version number of 2.1.5 in their filename. I haven't opened them in-game yet, but this is usually due to incorrect versioning in the build.gradle file

This was a misunderstanding on my part. I hit the "download most recent" button on curseforge and expected 2.2.1, but got 2.1.5. There is no issue with the versioning itself.