Refresh All - having built a workbook, looks like its become corrupt as I can no longer refresh

Analysis for MS Office Ver 2.7.300

I've built a workbook with 5 Data Sources in it, I have been refreshing as I was building it without an issue. I saved the workbook on my desktop (MS Office 365) as an *.xlsx file.

This morning when I open the workbook, the Refresh All option on my Analysis ribbon is greyed out. I dont get any error messages when opening the workbook.

Analysis is working fine, I can insert a new data source into the workbook, save it, reopen it and that data source will refresh but the connectivity from all the other data sources is gone.