Flow / Power Automate won't load on Excel Online

I have a flow that has been working for months, and suddenly whenever you enter the document online rather than on the desktop app it won't allow you past the sign-in page, this is happening to all users that have access to the flow and normally use it.    Using the sign-in option below doesn't do anything it just confirms that you are signed in. 

I've

removed the flow add on and re-installed it,

Confirmed it's still working if the workbook is opened in the desktop app. 

I've even tried creating a whole new flow,  which again shows in the desktop app but I can't get past the sign in page below to view it in the online version.. ?

Any assistance gratefully received.