Bird of paradise - leaf turning translucent then brown

tom.mcgraw92

I have a white bird of paradise that I purchased earlier this year which has 2 plants in the pot. The leaves on one of the plants have recently started getting patches where it goes translucent and then starts to brown. It's happened fairly quickly on 3 of the leaves, with one more affected than the others. See some pictures below. As it's happened fairly quickly, it's difficult to say how it will end up, but one of the patches is starting to dry out a little so I guess parts of the leaves are dying off. 

Would anyone have an idea of what could cause this?