error WIX0095: Multiple primary references were found for Feature 'TestUpdate' in Feature 'TestApp' and Feature 'TestApp' about issues

[bevanweiss]

Do you have your 'Common' project configured as a WiX Library?
Or do you have two MSI Package projects that you're trying to link together in some weird way?

It sounds like you should have your 'Common' as a WiX Library, and then have a reference from your 'Setup' MSI Package project back to your library project.
If this is how you have it, you weren't very clear.

You've got a very confusing arrangement. Why does your library define what Icon is used for the MSI Package?
More common would be that the library contains just references to perhaps a Feature 'sub-tree', with components etc under it.
Then from the main MSI Package project you'd reference in that Feature sub-tree with a FeatureRef link.
Or it might just get linked in through a ComponentGroupRef (if the MSI Package isn't really using Features).

[barnson]

This screams for a minimal reproducible example as an attachment or GitHub repo. Features in .wixlibs work but there are lots of moving parts in your post that we can't reproduce (e.g., merge modules).