I hacked around in there to add some quick logging, and subsequently updated my requirements.txt to install a newer version of the affected package.
I see the newer version being installed in the logs, but the files in .data/venv/lib/python3.7/site-packages are unchanged.
Can I just nuke .data? Will it be recreated?
I probably wouldn’t nuke .data, are you using virtualenv?
Yes, start.sh does something like (simplified):
VIRTUALENV=.data/venv
pip install virtualenv
virtualenv -p python3 $VIRTUALENV
$VIRTUALENV/bin/pip install -r requirements.txti would copy the venv folder beforehand, or export as a backup
Just a note, for anyone who wants to try this — if you copy anything out of the .data folder, it will be committed to git, cluttering things up if you check out your app via git, and taking up project space. Good luck getting your entire venv out of your git history 
@jean If you need to remove a folder from your repository, git filter-branch --tree-filter "rm -rf venv" --prune-empty HEAD (or --prune-empty -- --all)!
In the future, you can always move your .data folder to /tmp. Just remember to move it back if you need the contents because /tmp is, well, temporary.