Having been through due diligence for 3 start up sales, I will tell you 100% if you have GPLv3 code you are going to have a fun time justifying how it hasn't made your software FOSS.

Ive seen auditors with automated license software now that will find any GPLv3 code and dump it all to a CSV for you to discuss.

Someone left a GPL v3 license in one of our repos and it started an interrogation.

Maybe lawyers are overreacting, or maybe they don't want to fuck around and find out.