I believe this is an issue with your specific solution. Likely, because it is from an older version, the upgrade process is encountering an issue and is getting stuck. I would suggest that you open a support request. They should be able to assist you in getting it upgraded.
If you would rather try on your own, then upgrading the solution to interim versions of 8.X before going to 19.1 may work. I would try opening in the latest 8.0.2062 build and see if that can open it. If it does, you'll likely have no issues with 19.1.