Nik Silver Efex Pro 3 in its current form is crashing and is so slow as to be unusable.
Maybe a good idea to contact support?
I actually use it quite rarely. But just tried and exported to it and all fine. Not slow and did not crash.
But that was just a quick try, not really edited anything. Just used the presets. Also got a message, new version available. Updated, see screenshot for latest version.
I tried it again today and all seems good.