Recently picked up a tidy used A7r and took it away to Spain with me the other week.
I took it out of its bag one day and noticed these marks on the rear screen, they weren't there when I received it or earlier in the holiday. I haven't dropped or knocked it, they aren't cracks. Kept it away from moisture as much as possible, put it down on tables gently and put it in the bag when I didn't want it out.
The only thing I can think is that it sat exposed to the sun one afternoon when I was out on the veranda. Was only 10-15mins exposure, I think, and I moved it as soon as I realized. I didn't notice any marks then and it wasn't hot, I remember checking. It was the next day I noticed them so thats what makes me think that the sun has maybe done something to the glue.