Got these headphones last night, they worked great, this morning suddenly the noise cancelling has noticeably dropped in quality. It will block out a quiet hum but everything else I can hear as clearly as a normal pair.
I've updated the software and tried a product reset to no avail
@melekyeUpdating the software likely caused your 'issue'. This has been going on quite some time and has been reported here by dozens if not hundreds though it does not happen to everyone. I have updated to 4.5.2 twice and my ANC is still fine. Bose has done an extensive study though the customers who come here have different contrasting conclusions and so the 'saga continues'. There are two pinned posts on this topic at the beginning of this forum - one with the study and one with the discussion.
Bose currently offers a downgrade which may or may not solve your issue. Other than that, your only other option is to exchange your QC35 with Bose or elsewhere if you can and DONT upgrade the firmware. (Put the phone in airplane mode before you start Bose Connect).