With the latest update, selecting a color causes the the paint preview to show up, but you loose access to the color picker (it scrolls up to the preview section and you can’t select colors at the bottom of the color picker. It’s even more obvious when trying to select roughness or meltaness.
I don’t reproduce any of that.
What is your device?
Are you using a pen or your finger?
If you can do it, a video could help.
Might be a little unrelated but talking about materials, I just noticed that with the new update the opacity value on an object gets reset to 1 when closing and reopening a file.
Argh indeed, fixed for the next release.
Thanks a lot Stephane! 
I have a 6th gen iPad
Ah ok, I’ll fix that but until then simply add enough material preset to have at least 3 rows.