DS18B20 in parasite mode provides intermittent values

I am getting crazy with this:
I have 3 DS18B20, connected to GPIO 4 of RPi, with Hassio on it.
The connection is in parasite mode: Data Wire and Vcc connected to the central pin of the sensors with a pullup resistor between Vcc and the pin, external pins grounded.
I have added the 1Wire line in the config file:
The values that I get from the three sensors are OK but sometime they jump to 85°C (end of scale).
I have tried several resistors: 220Ohm, 1KOhm, 2.2KOhm, 4.7KOhm, 8.2KOhm, 10KOhm but the problems always happens.
The sensors work fine if connected with 3 wires (deleting the pullup=y from the config file).
They also work fine in parasite mode when connected to an Arduino UNO device: so the issue is not with the sensors.
Any clue?
I am really getting crazy…