Strange, looks like its working correctly 60% of the time and its failing 40% of the time.
When its failing, it appears to me as if the X and the Y are collapsing, the same amount, at exactly the same time.
No problem with the Z axis or the CRT high voltage.
The X and Y, display D/A converters probably have a common Reference Voltage?
If this common D/A converter Reference Voltage is collapsing (40% of the time), then you could end up with your symptoms?