Strange behavior of the mcp23017 i/o expander's inputs

Hi guys,
I have a very strange behavior of the mcp23017. I have set the input to PullUp. I have also measured this. There are 3.3 volts present. The mcp23017 pulls with standard 100 kOhm. That should be enough by far. Nevertheless I have switching sequences again and again, although I have physically connected nothing. So nothing should change. But it does nevertheless again and again. Has anyone had the same experience?

binary_sensor:
 # float top (if closed then out of water)
  - platform: gpio
    name: ${acronym} float top
    id: float _up
    pin:
      mcp23xxx: mcp23017_hub
      number: 1
      mode:
        input: true
        pullup: true
      inverted: false
    filters:
      - delayed_on: 100ms
log:
[11:54:24][D][binary_sensor:036]: 'AQLU float up': Sending state OFF
[11:54:24][D][binary_sensor:036]: 'AQLU float up': Sending state ON

Hi Gabriel,
I have th same problem. Did you solve it ?
KR Rafal