Found a very interesting post from johnss from 5/12/2020. Seems he's been examinng LP's with a microscope and seeing these cantilever gunkies: to paraphrease his post (thank you johnss):
"Have looked into this for a long time and taken many microphotographs of LP / vinyl groove surfaces.
first you need to understand what is mixed in with vinyl pellets before the record pressing plants ever sees them. Many think mold releases are used. Have not found that to be the case.
But during PVC pellet processing, Calcium carbonate is added to almost all vinyl formulas during formulation as a processing aid for all the manufacturing steps, from extrusion, to pelletizing to molding.
during the record pressing cycle, the calcium carbonate is still in suspension in the PVC vinyl matrix during the heating cycle. During the cooling cycle, the rapid change in temperature causes the Calcium carbonate to migrate to the the cooler surface, collecting in the bottom of every groove.
As the stylus tracks the groove, the bottom of the stylus is hitting the tops of these larger particles. Want evidence? Take a look at the bottom side of your cartridge. you will likely see some fine dark white to light tan tiny particles clinging everywhere. these are tiny calcium carbonate particles the stylus removed from the bottom of the groove.
Have looked at over 300 records under a microscope and have never found one without the deposits."