Ampersand Issue – External and Internal Links not working

Hello from Germany,

Since a few days I am experiencing trouble to call amp pages from the browser in WP.
if I address a Page directly, I get an error due to a mistaken ampersand at URL.

e.g. https://www.izp.de/?page_id=1 leads to https://www.izp.de/?page_id=1;&amp=1
in mobile view.

The problem experiences
– by calling amp pages externally (browser or htaccess 301)
– internal WP 301
– buttons and links within HTML

So far the problem does not seem to come up
– by calling from sites main menu (Generated AMP view)

Could you, please, try to fix it?

The suggested WP ampersand fix in formatting.php does not change anything.

Many thanks for your kind help from Germany
Reiner

The page I need help with: [log in to see the link]