td2 Thanks for your reply. As far as I was aware there was nothing near my phone, I just had it in the living room. I had also been told a new screen cover or if it was somewhere hot then that could affect it, but none of these things were applicable.
It was all very strange and definitely had me on edge as it was my banking app. Hopefully it’s more a hardware issue than security.
Have you installed many apps, especially from non mainstream sources? This could possibly be a virus / trojan attack. It might be an idea to do a full scan with an anti-virus app - I use Kaspersky, but several other good, free ones are available, such as Eset, AVG, Norton, Bitdefender, Sophos, Malwarebytes, etc.