The minimum pool diff is set to 42. Previously if you set a worker diff in the web site and then set it back to zero it would stick to the worker diffThat has been changed now and setting it back to zero will set it back to default and allow it to get as low as the pool allows - during a ramp up or ramp down of hashrate it might now be dropping diff to lower levels. Presumably if the lowest diff you can have is 127 on NH you will have to set it to 127 or higher for rentals with them now, but I'd suggest a sensible much higher value as you've done. Use hashrate in TH / 1.4 for the worker diff.