Hi, thanks for your support!
I’m using version 8.6.1. I tried to downgrade but 8.6.0 is no longer available for download. Do you have a copy of that?
I have enabled the legacy checkout experience and now the fields are normal. No custom css added that can affect the checkout fields.
I don’t think it conflicts with another plugin. I didn’t add any new plugins.
It is a live website and I can not switch themes.