Recieved this after contacting UBS:
We are contacting you regarding your feedback about the Graphene OS operating system.
UBS maintains the highest security standards, and protecting our clients as well as the security of their assets is our top priority.
UBS Mobile Banking only supports operating systems that can be fully validated within our security framework.
Alternative operating systems, cannot be verified through these checks and will therefore no longer be supported.
We apologize for the inconvenience and thank you for your understanding.