Unfortunately I wasn’t able to reproduce this issue with the repro steps you’ve provided.
In 4.18, I created a new project, then created a material with a material function:
I made sure all textures were set to “Shared: Wrap” except for the texture being used for the Normal, which was kept as “From texture asset.”
Here you can see the Material Instance and the scalar parameter values I entered, along with the resulting scene.
Next, I saved the project and opened it in 4.19 and all the scalar parameter values were copied over correctly and the scene looks as expected.
Please let me know if there is anything I’ve missed.