While an application compiled with ArcGIS Pro 2.7 should work with ArcGIS Pro 2.8, if users recompile a solution hard-coded to use the 2.7 dynamic-link libraries (DLLs), it does not work. After removing the hard-coded references to the 2.7 DLLs, the issue no longer occurs since the application references the ArcGIS Pro DLLs that are installed on the machine running the application.