Any chance you are running Mojave with an APFS drive? If so, I have had the same problem. BootCamp Utility does not seem to like seeing the boot drive as an APFS drive. When I was fighting with it, I had to reformat the Bootcamp into APFS and eventually get each partition to merge into one. I strongly suggest that if you take this path, you back up all crucial data, and do not play risky like me!
Any chance you are running Mojave with an APFS drive? If so, I have had the same problem. BootCamp Utility does not seem to like seeing the boot drive as an APFS drive. When I was fighting with it, I had to reformat the Bootcamp into APFS and eventually get each partition to merge into one. I strongly suggest that if you take this path, you back up all crucial data, and do not play risky like me!