The only time that my Starling card hasn't worked is in the French motorway tolls (it works fine in the motorway services), where it thinks I'm somewhere else. I keep meaning to contact them about it, but invariably forget when I get home.
Starling disables magstripe transactions by default so you need to enable them in the app (and then it turns them off again a fairly short time - 48 hours according to its Twitter - after last use). Guess what the toll machines use ...
Thank you, that's worth knowing - although I don't know when I'll next need that knowledge (next years odyssey was already planned not to use motorways in any of the 5 mainland European countries through which it will pass). I'll go and have a play now though, then when I do need to know I should be able to remember.