matt_dt3d

Update and solution:
I have received my printer back from the Ultimaker Service Center. They replaced:
Sliding blocks (maintenance) Timing belts (maintenance) Printhead Cable (broken retention clip) Printhead PCB (the threaded insert was about to break off) Printhead capacitive sensor (the old one had a loose wire) Front Axial fan - (updated to the new version) Nozzle seal - (maintenance) Both Printhead side fans (the slack wires were hanging out of the back of the print head) Printhead side fan bracket (had a chip on the bottom) Both Bowden tubes (maintenance) Both Feeders (maintenance / update to the new fine-knurled version) Installed a new AA 0.4mm PrintCore (maintenance) Front Axial fan (again - the other one died during testing) And the test prints they ran were turning out well.
 
However, upon receipt of the printer, I was still having the wall separation issue, no matter what version of Cura I used (I tried 4.13.1, 5.2.1, and 5.4.0).
 
The fact that the issue was still occurring and was happening on my other Ultimaker machines led me to investigate the PC I was using to slice the files. All of the hardware is recent except the graphics card (an ASUS GTX 660, model GTX660-DC2O-2GD5), so I purchased and installed a new graphics card (an MSI GTX 1650).
 
Now everything I slice is printing fine.
 
So, a lesson hard won: the graphics card you use in your PC for slicing matters!