Hi all,
In general, there is not a generic issue with HAOS 16.0. We’ve tested it in many configuration successfully. We had about 1600 installations on the beta channel testing the pre-releases successfully. I’ve updated my Yellow with CM5 to 16.0 yesterday successfully. That said, it does seem a bit strange that there are multiple reports with update issues on Yellow, so we’ve temporary removed the release from stable channel while investigating.
It seems that there are slightly different outcomes.
@ace_archer are you using CM5 as well? Which variant exactly?
@xstrex can it be that maybe you have two HAOS installations, one on the internal eMMC and one on the NVMe? 
Can you check the output of lsblk and blkid.
@mike15 and any others with non-booting system: Can you attach to the serial console to see if there is any boot log which could help us better understand what did go wrong? This gives access to the HA CLI.
These two links have step by step instructions to hook up the serial console: