I suspect it will get added in due course, it sounds like a blip to me. But in case it doesn't if you use BA.com on your phone via Chrome / Explorer then that works Boarding Pass certainly at the larger airport in London and domestic. Alternatively email it to yourself and then use your PDF viewer. You just show the barcode rather than QR code, screenshot it if you like, and it all works fine. I even saw someone using the Kindle App to display the PDF boarding pass, no problem there. At smaller airport they may be a bit grudging about it at security.

At LHR, LGW and LCY (and a diminishing number of other places) you can also reprint your boarding passes at the airport if you get time, the kiosks do a reprint service.