I've just found this thread after having similar problems. I've had Barclays, Barclaycard and Pingit apps installed on my Umi Super since buying it, firstly with no issues. Umi then updated to Android 7 a while back and all three failed to run (just get an app has stopped warning). Barclays were, unsurprisingly, of little help. As the previous poster said, Barclays and Barclaycard apps updated a few days ago and surprise, surprise they both worked again (no such update for Pingit).
At first I thought maybe the system update to Android 7 is "rooting" the phone but 3 other banking apps I have on there worked fine.
Unfortunately the Barclaycard app received another update last night after they realised they may have fixed it and it now has reverted to not starting again. I'm just waiting for them to break the Barclays app now.
One other thing, when they started working again they both acted as if I had never used them before and I had to fully re-register my bank/card details with both apps.