Updating from LINUXCNC - 2.8.4-23, Mint 20.3 - gmoccapy lathe structure

Before I had a serious accident with a mouse that resulted in a 3.5 tonne Shizuoka mill turning up at the house, I converted my Bridgeport clone to CNC using a Chinese all-in-one controller from Newker. Those things in the photos are for the z axis drive, housing the closed loop stepper, timing belt drive and pulleys. I fitted a 16mm ballscrew where the original feed trip adjuster screw used to live, as this is much neater and robust than the usual arrangement with a ballscrew cantilevered in front of the head and required minimal modifications to the head. The top one is the final iteration.
Here's a picture of the basic mechanism, before the limit switches, encoder scale etc were fitted (otherwise you wouldn't see the ballscrew).
 
You inevitably lose some of the precious z axis travel due to the limit switches etc but I managed to minimise that and retain most of the 5" motion.

Anyway, back to the problem in hand. When I run my installation, I'm getting a lot of missing content in the "cycles" tab:
 

And the command line errors currently look like the contents in the attached text file.
 
It looks as if there is something seriously wrong in the Gtk / python / gladevcp bit. Could somebody suggest how I might troubleshoot / resolve these errors?
LinuxCNC seems to run OK but the macros are still not showing up. Many thanks.