A Non-Existent Background Rendering Issue

I have a few clips in the time line that I have speeded up and have chosen the Machine Learning retime quality setting. Every time I export this time line, I get this error message:

However, if I cancel this and open the Background Tasks window, there is nothing going on.

If I choose CONTINUE, the exported file is fine, and the speeded up scenes play properly in high quality.

What's going on here?