Some test CRTs are purpose built without dag because they are different sized than the original...The dag ground spring on the chassis probably won't touch it. If the spring isn't touching it the dag goes from a filter cap to a floating HV source for nasty static jolts and possibly a noise source.
When dag isn't grounded it tries to arc to ground and or put out Corona (the static to air discharge, not the beer, the virus or the mythical beer-virus
) both of which create electrical noise that can disrupt the set....it is worse when the dag is flaking creating dag islands or the ground spring contact point dag is the damage point because floating conductors at different potentials in close proximity make stronger more frequent arcs than distant ones.