Why does loading TextMeshPro material from Asset Bundle only partly work?

We recently started using asset bundles in our project. The bundles work fine, we are building for iOS and Android targets.They are being built for respective target devices. Everything works fine except for 'some' Text-Mesh-Pro materials. utilizing DistanceField material/shader.

The material does not technically break on device.... you can still read the text and it is still using some kind of TMP shader as the distance field must be working, but various features of the material are gone (on device). For example... material that uses a texture gradient... is missing the gradient on device. another example... material that has a border/bevel, is rendered without the bevel, on device. This includes old or new devices such as iPhoneX

This feels like the shader not having all variants, or failing to compile fully, maybe using a fallback shader, or forcing game to use mobile shaders when on a mobile device ?

I have tried including all TMP shaders in graphics settings. I have tried making a shader variant collection, and adding it the bundle, without success.

Does anyone have any ideas as to what is going on? Thanks !