After starting Pegasus I can click on several (it varies) messages in the Message List , this happens on any subsequent. I can dismiss it clicking on OK several times (it varies). After that nothing is visible in the Preview Pane. The only way to deal with it is closing and restart Pegasus. The behavior is also the same running Pegasus by another Windows user and in safe mode; and it's the same after uninstalling Pegasus, including removing all references to Pegasus in the Windows Registry.
In case it helps, I'm using Win 10 ver 2H22 build 1904.2846.
Larry Hess CPA | Albuquerque NM