The Sequel Viewpoint software is installing an older version of Newtonsoft.Json into the .NET global assembly cache. This is forcing Designer to load the 12.0.0 version of the Newtonsoft.Json.dll from the .NET GAC. Because Designer uses version 12.0.1 it is causing random errors when loading.
Message: 'Newtonsoft.Json.Linq.JObject' does not contain a definition for 'UseClassicMode
Download the 12.0.1 version from the link below and use the .net45 version and copy it over the 12.0.0 in the C:\Windows\assembly\GAC_MSIL\Newtonsoft.Json.
NuPKG files are just zip files, so anything that can process a zip file should be able to process a nupkg file, i.e, 7zip.