I have spent hours with ChatGPT trying to fix this.
I run a blog site. Desktop single posts load correctly on all devices.
The home page loads correctly on mobile devices.
Single posts default to the “jevelin” header and I have been unable to find any way to correct this problem. Mobile devices obviously should load a header appropriate to the website.
This kind of issue is often caused by the AMP plugin, which loads a simplified version of your pages on mobile and can override theme styles. Could you please check if you have AMP (or a similar plugin) installed and active?
Let us know what you find, and we’ll gladly help you further.