Created a ReFS volume on Windows 2016 and it mounted fine and I wrote stuff to it - detached the drive mounted on Windows 10 it mounted and everything was fine - I wrote additional files on it and mounted it on Server 2016 again - Showed up as RAW. I guess Windows 10 doesn't support certain ReFS features and downgrades the drive to an earlier version or something?
According to the mountability chart in this link https://gist.github.com/0xbadfca11/da0598e47dd643d933dcWindows 10 upgrades ReFS 3.1 to 3.2 which isn't supported on Server 2016 causing the drive to mount as RAW
Registry to prevent upgrade. It needs to be set before connecting. I do not know how to downgrade anything that was upgraded.