Most Financially Damaging On-Set Mistake for Indie Post-Production?

Hey everyone, I’m typically on the music side of things, composing scores, but I've been getting more involved in the production workflow for a lean indie feature I’m scoring. We shot mostly on an AMIRA with some B-cam stuff on a Pocket Cinema Camera 6K G2, lighting with a couple of SkyPanel S60-Cs and an M18. We tried to be super diligent, but I know on-set oversight can really bite you later.

I’ve been trying to educate myself on common mistakes to avoid in future projects. There are tons of articles about on-set errors that wreak havoc in post, everything from poor reference data to not getting clean plates for VFX, or bad audio recordings despite having an 888 and MKH 50s. My question to all of you experienced filmmakers and post-pros is: out of all these potential on-set blunders, which single mistake would you say ends up being the most financially devastating in post-production for a typical indie film budget?