OGS on Chrome appears to be working again. 
But what I find interesting is that during the ‘Intermittent server issues’, other browsers continued to work. Safari for GaJ and Internet Explorer 10 for me. There has to be a big clue as to the nature of the problem there.
Actually I find when Chrome is slow to load OGS or when I am getting repeated ‘Error submitting move’ messages, IE10 is consistently quicker and more reliable. However; IE10 is clearly not supported on OGS as many of the features simply don’t work or work incorrectly. Fair enough. I wouldn’t expect devs to prioritise compatibility with such an old browser. So my question, for anyone who feels competent to answer it, is:
What’s the best way to run OGS on an old computer? (In my case one with Windows8 and a very limited USB mobile broadband connection.) New Thread started as per BHydden’s suggestion.