I ended up trying to raise a support ticket on this - I filled in the online form after going through the Troubleshooting tips (except for unlinking/linking the tree which isn't a tip for media sync problems) and uploaded the SyncError logs I generated.
After more than a week, I've had a reply saying to go through the trouble shooting tips! I'm currently relinking my tree as I've unlinked, I'll post later what happens.
After more than a week, I've had a reply saying to go through the trouble shooting tips! I'm currently relinking my tree as I've unlinked, I'll post later what happens.