This means, ccx is in trouble finding a convergent iteration sequence.
Unfortunately ccx builds for windows are less stable than native linux builds (so they say).
I've tested several builds against stability under iterative load, and there are differences!
Don't know which build is bundled with FreeCAD, but i can confirm your results.
If you are running into problems, please try this:
https://github.com/ddfem/ccx_mingw64/bl ... 2_MTNO.exe
most stable because of non optimized code
Much less faults on ccx's test suite!
In single thread mode it will finish.
Unfortunately we have no analytic result for this example, so we couldn't do any verification.
But at least a hint to get this work with bundled ccx.exe:
Change degree of elements from 2 to 1 (most important!!)
For better results refine mesh at least to max size 10,0