Hi Rik586,
It sounds like you are close to getting your access database published and synchronized to SharePoint Online Office 365. The following links detail the process you are going through and provides recommendations concerning setup and configuration. You can refer to the following help article for the detailed information:
How-to Build and Publish an Access database to SharePoint
How-to Build an Access database to Share on the Web
In addition, I'd like to confirm how long since you encountered this issue? I suggest you check the service health in your Office 365 admin page for any related information. Besides, please also check if there is any planned maintenance information related to SharePoint online.
Thanks,
Allen Qiu