Hi Gareth, a screendump would help to give you a better answer, but there are some iOS quirks when building apps. Anyways maybe it's the Simple Menu widget that causes this, see last paragraph here:
https://github.com/mendix/hybrid-app-template
In our app I added the bottom property in hybrid app styling:
.mx-hybridapp {
position: absolute;
top: 0;
right: 0;
left: 0;
bottom: 0;
bottom: calc(0px - constant(safe-area-inset-top));
bottom: calc(0px - env(safe-area-inset-top));
}