I suspected that was it! Confirmed that the .1 works for me as well.
I don’t believe 0.28.01 is valid, per semver.org: “Numeric identifiers MUST NOT include leading zeroes.”
Interestingly, sometimes PIO will fail silently when I use 0.28.01 via lib_deps (no error message), but it doesn’t install the lib dependencies at all. When I change it to 0.28.1, the dependencies install properly. I’ve reported on the PIO community because I think that the error handling could be improved.