TextMeshPro/RectTransform GameObject localPosition is being reset

I just tried upgrading to unity 2018.1.3 from 2017.1.3p4, and I am having an issue with TextMesh elements where transforms are being cleared. This appears to be due to the attached RectTransform and what appears to be either a bug, or at least very odd behavior?

I am creating gameObjects in code, attaching TextMeshPro behaviors to them, initializing various layout things, and then positioning them by setting gameObject.transform.localPosition.

In the past, this has been working without...

TextMeshPro/RectTransform GameObject localPosition is being reset