Also keep in mind that preview and stable versions use different nuget package folders. Could it be that you simply need to re-install some packages? Like Sebastian said, have a look at the Debug window first, it should tell if packages are missing or if there are any other errors due to different versions of a package in preview and stable.
Alright, there acutally were some build errors even before exporting and I fixed those. So the export was going smoothly but the app still crashed silently right after being started.
The preview build export still worked. So now I copied all the nugets from the preview folder to the stable release folder and now everything works as expected.
Not sure what was the issue here, it seems maybe some outdated nuget was picked up, but no idea which one and what the error really was…