The fact that the app is looking for pngs in this folder (http s://arbgisapps.ad.arb.ca.gov/webappbuilder/apps/3/widgets/About/images/icon.png) tells me that something went wrong with the download of the app from WAB and subsequent publishing of the app to your web server. The apps/3 is only a folder that would be available in WAB Dev machine and should not be referenced on the web server. Did you download the app from WAB Dev and then extracted the zipped app to your web server?
The other errors about woff and woff2 are due to you not having those MIME types registered with your web server.
I am having similar issue of widget icon not showing in webappviewer. I am getting following error in inspect window:
https://[mymachinename]/webappviewer/widgets/MyFirstWidget/images/icon.png?wab_dv=2.21 404 (Not Found)
I was able to see my icon when I copy pasted my icon image in Image folder of my widget. But after I tried to edit/save the image, I don't see it anymore. I am trying to fix the path of the image but cannot figure out how to do it. Anyone knows how to fix this?