I think the case why you are not seeing the UTM parameters not working, will most probably because of the following reason:
You may added the PWA to your Homescreen while installing our plugin, and before Activating the UTM Add-on.
Upon this case, once you activate the UTM Addon after adding the PWA – the UTM parameters won’t get added to a earlier added PWA. PWA is functioning with the help of manifest. Once you install PWA, the manifest may be cached upon your device.
Upon your case most probably as you haven’t added the UTM initially, the UTM parameters may not be added to the Start page URL and due to that there’s a chance that all the hits are showing as direct.
If you made any changes to our settings like changing of Icon, Start Page, Application Name, Short Name, UTM upon our settings it won’t get replicated upon the manifest instantly. It may take 24-48 hours, sometimes even more days or weeks – based upon the caching.
Steps to easily troubleshoot the issue
a) First of all you need to uninstall the PWA already added upon your device.
b) Clear the browsing data and cache upon your browser.
c) Visit the website again and add the PWA from the prompt.
d) Finally Check the Google Analytics.