Grandad:
Optional, but it would be informative if you ran the special report that is attached to show exactly what your Custom Column configuration is from a technical perspective. If there is something corrupt about your problem Custom Column, this should show it.
The Calibre plug-in that hosts that special technical report is found at:
https://www.mobileread.com/forums/sh...d.php?t=269911
The attached image shows the menu path.
The version of the plug-in that contains this report is 1.0.77.
DaltonST