Well to be precise it is from public beta 3 which I assume is the same as Dev4. I think they removed "Store Messages in iCloud" and the switch. I am guessing my sync now implies this will not be an option going forward and it's the way it will be when you turn on messages under iCloud settings. I assume you have done this? Have you done this on all your devices logged into messages? Are all these devices on beta? For me, I am running iOS 11 and HS PB3 on my MBP.
Try login out and in of Messages on all your devices. Same for iCloud and also flip the Messages switch a few times under iCloud.
So something I have noticed and not sure if its a bug or not. My messages sync. Took a while but they did. Something I noticed is ... I have IOS11 on my ip7+ and IPP. I do not have imessage turned enabled on my ipp. Never had it enabled. Prior to beta 4 if I opened message app it would ask me to log in. Now if I open message I get the same prompt to log in but now it shows all my text messages from my iphone. I don’t want them on multiple devices why I left message off. Is this the way it should be working? I am unable to delete those messages. Screen shot..
For those that have synced, and then restored as new and used iCloud to sync your messages: Did the pictures in your messages restore? My messages slowly seem to by syncing, but the pictures or pics are not.