After upgrading to 2019.1.2f1, some UI images are changing size

The strange thing is, although they are changing size, the scale and rect transform values aren't changing. Selecting components in the inspector will show no difference between an image which has reduced to 50% of the size from one which has increased to 120% of the size.

This has only happened from the final 2018 unity build when upgraded. I think it must be to do with the new UIElements but can't find anything specific which might be causing this. Any help would be really appreciated as I feel like I'm banging my head against a wall trying to fix it. I can get screen shots of examples if needed.