Debian 9 support will end on June 2022, and SRE rightfully asks to avoid running on a non supported OS for Production traffic/infrastructure.
Migrating to Debian 10 means also upgrading to Python 3.7, something that we should be able to do (in theory) without re-training all models (pickle's main format doesn't change between 3.5 and 3.7 for example).
We should try to review what is needed to upgrade ORES to Python 3.7 and Buster (Debian 10), and define a strategy to roll it out. It will drain some time from Lift Wing, but we'll gain ~2 more years of OS support from upstream.