is varnish cache not clearing when new modules added?

[keithbentrup]

from user report:
I’ve added a module to app/code/
The module includes Less files
The Less files get copied to /var/pre_processed & compiled to pub/static
However, frontend is still showing original styles.css (browser cache cleared, etc., etc.)
Any server-side or browser command doesn’t load the new file
Except restarting containers (my understanding is restarting a varnish container clears it’s cache)