Hi, those all looked fine, but we seem to have uncovered a fix.
If user creates a new library and then copy pastes workflow files (which use deserialise json activity) into the project, UiPath will flag the validation error (unknown activity). User then adds Uipath.web.activities to dependencies which fixes that error, but will the library will now crash when the user publishes the library.
To fix, just add the dependency before you copy paste the workflow in. Then it will publish fine.