Auto Settings shortcut (Control+U) in LR Classic 13.3 in Develop mode: Broken?

Another, probably related, issue: Control+Shift+U in the Develop module does not apply "Auto white balance" to the selected image(s), as both the LR Keyboard shortcuts page and the Develop module pop-up indicate it should.  Instead, the status bar at the top of the screen says "Preparing files for disc burning," followed by a dialog that says "Lightroom cannot burn data because it cannot locate a drive that supports burning."  (I do not have an optical disk drive permanently connected to this machine.) It seems to be invoking the Export... to CD/DVD function rather than applying Auto white balance. From this I surmise that the previous Control-U behavior was actually invoking the Export... For email (Hard Drive) lightroom preset (which by default resizes images to 640x640 pixels max and outputs a .JPG with the original filename).

Curiously, after dismissing that dialog, when I return to the same image and press Control+U, it does in fact apply Auto settings to the image.

Control+U when pressed in the Library module does appear to apply "Auto Settings" to the selected image (though it is not listed as a shortcut for that function in the Control+/ popup for that module, or in the section of the LR Keyboard shortcuts page associated with it).  I would like it to do so in the Develop module, as advertised.

Also, the .JPG file exported appears to be inetnded to be used as a thumbnail (it is 640x427 pixels, whereas I am working with a 5760x3840 original CR2 file).  

P.S. - When I press Control+U and choose a folder, the selected image (in this case a Canon CR2 RAW file) is exported to the specified folder as a .JPG file using the original image filename (i.e., apparently not using any export preset and its file naming/renaming specifications).

Also, a correction: the LR Keyboard shortcuts page describes Control+U as "Auto tone" rather than "Auto settings," but I believe it is referring to the same function.