Unable to rebuild/install a local addon

I was using the addon ‘mediola2mqtt’ a long time now and it required from time to time a rebuild, so that it worked as expected. Recently I also tried to rebuild the addon, but the process failed with the error message:

The command ‘/bin/ash -o pipefail -c pip3 install paho-mqtt’ returned a non-zero code: 1

I tried to reinstall the addon, but during install process the same error is showing up. The error seems to be in context with the dockerfile which contains the following code:

RUN apk add --no-cache python3
RUN apk add py3-pip
RUN pip3 install paho-mqtt
RUN pip3 install requests
RUN pip3 install PyYAML
COPY mediola2mqtt.py /
COPY run.sh /
RUN chmod a+x /run.sh
CMD [ “/run.sh” ]

Trying to run the pip3 installs within the terminal works without any problem.
This missbehaviour showed up, after I installed my new mesh router. No changes or updates in Homeassistant was made.

Any help would be highly appreciated.