Seems docSize needs to include the json part and the string storage. github.com/bblanchon/ArduinoJson/issues/151 For my 313 byte serial output the doc size is calculated as 152 so it is unlikely to be able to hold the information.
Weather Radio V 1.10 152 <=== Serial.println(docSize) { "Davis Anemometer": { "init": true, "direction": 87, "avg speed": 0, "min speed": 0, "max speed": 0, "rotations": 0 }, "BME280": { "init": true, "Temp": 14.42, "Pres": 1024.433, "Hum": 50.88184 }, "MLX90614": { "init": true, "T amb": 14.82999, "T obj": 14.19 }, "TSL2591":<Rni } }