That was the case for sure until I did exactly what you just said: Upgraded my computer to a fast SSD.
Now, back to my question: This only happens when I use the Sharpen Filter. The rest of the time it runs great, and I love using Shotcut. I let it work on it OVERNIGHT, and it still does the same thing. I also saved the project, came back to it later, and gave it plenty of time again. Same thing until I exported it.
Also, it took no longer than usual to export the project to an MP4 when this was occurring. So, I cannot believe that the Sharpen Filter is just so bandwidth intensive that it is supposed to do this, when everything else runs fine, if this is what you are suggesting.
Are any of you others experiencing this same thing?