I received these with firmware 2.0.1 which worked phenomenally with my Mac and iPhone. ANC was nice and bluetooth stable. Unfortunately, the google assistant app decided to update my firmware to 2.5.1 by it self!! Seriously Google? Ask me for permission first.
Afterwards, ANC got noticeably worse. I played various background noise on my speakers and there was no difference between low and high ANC. Bluetooth skipped every 2 seconds if both Mac and iPhone were connected whereas it worked seamlessly before. Symptoms didn't go away after updating to the 3.1.8 firmware via Bose's website. These are getting returned.
If you get these headphones, DO NOT update them - please. If it ain't broke don't fix it.
Notes: -I did the Bose reset and re-paired multiple times. No dice. -This ANC issue happened on the original QC 35 too -google assistant initiated update WITHOUT prompting "yes or no". This happened when opening the app.