I just upgraded from Onprem 8.2 to 9.1, which worked fine.
However, I noticed that my customizations are not applied any more. When I check the solution layering, I see that there are 2 Managed solutions on top of my Unamanged layer (Active). I tried to export my Unmanaged solution and imported it again, but same problem. Also I have tried to press "Publish All", but same problem comes.