I have just seen a problem which I first assigned to qcustomplot. Finally, the issue was not caused by qcustomplot
and I solved it. This is just for your records.

System: Windows 10 with an Intel HD Graphics 530.
Symptom: the qcustomplot widget causes a segmentation fault on the first replot.
Callstack sais that the location of the crash is in dll "ig9icd64.dll" (in Qt5Core in qtcustomplot).
The crash did not appear if deactivating opengl options on startup.
Solution: Some older Intel OpenGL implementations seem to be outdated. I updated the
Intel HD 530 driver and the problem was gone.

Best regards