I ran into this issue and asked about it on Slack - it was suggested to me that posting the solution here might be helpful to others who have similar problems.
After upgrading to 0.12.0, I suddenly faced this issue on attempting to connect to a BigQuery database. It turns out the issue is related to snowflake-connector-python - a specific release of that package has a bug which causes it. There is some detail in this stackoverflow answer.
It can be resolved by installing a later version of that package: pip install snowflake-connector-python==2.3.1.
Weirdly I didn’t run into the issue in connecting to snowflake, only BQ - but for anyone who runs into it in future, it’s worth giving that a try.