I'm facing the same issue with my outdoor sensor. The Humidity is stuck at 100% most of time. If the temperaure goes up - like around noon - it goes down for some short time until the temperature goes down again and the Humidity jumps back to 100%. See image attached, blue line is the outdoor sensor. The other lines are indoor sensors build from BME680 or DHT22.
I'm using ESPEasy on a Wemos D1 mini with the sensor connected through I2C - see https://github.com/letscontrolit/ESPEasy/blob/mega/src/src/PluginStructs/P028_data_struct.cpp
Thanks for looking into this.
... I moved one of my BME680 sensors - using BSEC lib on an ESP32 - outdoors next to the BME280 for comparison -> see the image attached, turquoise line.
Another RF outdoor sensor from a commercial weatherstation is reporting ~60% relative Humidity at the same time 🙄