This was happening with one of our toilets. After replacing everything with all new parts, I came across one YT where the guy described a "siphoning effect" when the refill tube is too long or is positioned too far down to overflow. Sure enough, mine was both too long and too far down the overflow. I shortened it up to where there was only a little droop and only about 1/2" of refill tube going down the overflow. Worked instantly, and that was 3 years ago.

I'm not completely sure of the physics involved, but the refill tube was drawing water from the tank... to the point where the fill valve would open up to replenish the vacated water (ghost flushing).