TL;DR: https://bugs.python.org/issue42967 changed parsing behavior that prometheus exporter used to handle weird ISP router data.
I've been using https://github.com/mbugert/connectbox-prometheus to collect data from my ISP-provided modem/router. The provided docker image worked fine in December 2020. However when I recently tried using the docker image again it would fail to properly log in and result in an error.
First thought when this occured was an update pushed by the ISP that changes the login protocol for the router.