Discovery component not working / netdisco error

Hi, I just updated my HA on Raspberry Pi3 to 0.38.4. The discovery compontent stopped working. The error log shows the following line:
[homeassistant.bootstrap] Not initializing discovery because could not install dependency netdisco==0.8.3

I manually installed netdisco with pip3 install netdisco but this didn’t help.

Any idea?