Been using mt4 App on phone for a few months - all ok.
Last week I noticed it couldn't find 2 currency pairs when I searched for them - GBPCHF was one.
Today - I go on an open trade to try to close and it comes up with - invalid entry (as though I had put a sell entry on for a different pair) so I couldn't close my trade.
It might be broker stopped offering those markets, but I doubt it. Might be renamed though (GBPCHF.eur or something like that).
Try editing the instruments (first tab top right corner), you should see them somewhere in there if that's the case.