I do not think this is the case, because it is automatic and if you have earnings that you never received you can always write to them and ask. There is also a pay minimum on every person's profile, if the earnings are less than that minimum, they automatically transfer to the next pay period. "Stopped paying him" is not possible. Medium is not a mafia. But I do notice that the content on Medium is becoming more and more idiotic and toothless, because people have a lot of other alternatives where to write and use Medium rarely. So it is very possible that less people read you, you earn below your pay limit and not getting paid until the money accumulates.