facebook app photos display a grey border instead of black

Got my iPhone XS nearly 2 weeks ago, when I go to Facebook and click to enlarge pictures it brings it up, border is back, then after about 2 seconds it turns to this weird grey colour. I’ve restored the iPhone, reinstalled iOS, the app, checked settings, nothing I do seems to work! I also set it up as a new device with a completely new Apple ID and redownloaded the app, it didn’t work. The picture shows the grey borders so it’s not the screen and is the software that is doing it, help appreciated.