This probably means the degaussing circuitry is terminating suddenly instead
of gradually as it should. The most likely cause is a bad solder connection
to the degauss thermistor or posistor or something feeding it.
You can confirm this by manually degaussing the screen with the TV or monitor
turned on. If the problem disappears, the above diagnosis is probably valid.
Check for bad solder connections in the vicinity of the degauss components
and AC line input.