Software version has nothing to do with unlock. It's all the IMEI being flagged in a database by Google as being able to unlock. They all come locked, on first set up or after a factory reset they phone home to see if the have permission to unlock.It should still be unlockable though correct?
This happened to the Pixel 2s on a large scale on first release. Google fixed it in their end, but that was on new phones. This time it's different, it's on RMA phones. They are just shipping the wrong phones to you guys. Their RMA system is currently horribly broken it would seem. I hear rumors they went to a new system in early September and it has been a mess ever since.