The tracking opt-out feature may not work

Matomo 4.12.3
If Opt-Out is executed in my Joomla installation (own module iframe), the following message appears:
“The tracking opt-out feature may not work because it appears the opt-out popup has been blocked. Please refresh the page to check if your opt out status has changed.”
After the page is refreshed, the check mark is back in.
Since there are many identically configured pages and it only shows up on one page, I just can’t figure out what the cause is. Same browser with identical settings and extensions. Both Joomla installations plugins and extensions identical.

I also copied the tracking code 1:1 from the other module to the 2nd website, but success = 0.

Anyone an idea?