Extra website showing in Matomo dashboard in addition to the tracked one

I am using Proxy Tracker with latest Matomo, here are the specs:

• Matomo version: 5.1.2
• MySQL version: 10.6.20-MariaDB-ubu2204
• PHP version: 8.3.14
• Ubuntu 22.04

on a specific domain used for tracking matomo-server.com.

I am using this matomo-server.com to track multiple websites: tracked-domain-1.com and tracked-domain-2.com, by adding the matomo folder in the sites and using also the Token for the UserTrackingAPI.

Each of the tracked-domain-1.com and tracked-domain-2.com have the JS code added that looks like this:

<!-- Matomo -->
<script>
  var _paq = window._paq = window._paq || [];
  /* tracker methods like "setCustomDimension" should be called before "trackPageView" */
  _paq.push(['trackPageView']);
  _paq.push(['enableLinkTracking']);
  (function() {
    var u="//tracked-domain-2.com/matomo/";
    _paq.push(["setTrackerUrl", u+"matomo.php"]);
    _paq.push(["setSiteId", "hashed-value-here"]);
    var d=document, g=d.createElement("script"), s=d.getElementsByTagName("script")[0];
    g.type="text/javascript"; g.async=true; g.defer=true; g.src=u+"matomo.php"; s.parentNode.insertBefore(g,s);
})();
</script>
<!-- End Matomo Code -->

The tracked-domain-1.com is the first website I've setup on matomo-server.com and the primary domain.

The issue I have now is that inside Matomo's dashboard for tracked-domain-2.com, I am seeing clicks and URLs from tracked-domain-1.com:

Any idea what what's the issue and solution here?
Is there any way I can troubleshoot this to find what's causing this?

It's confusing to see 2 sites in the same dashboard : \

Thank you!

Start with the embedded JavaScript tracking snippet and the Matomo dashboard configuration for tracked-domain-1.com and tracked-domain-2.com. Reproduce the cross-site data issue using the supplied Matomo, PHP, and MariaDB versions, then inspect the tracker URL and site ID used for each request. Done means the source of the mixed site data is identified and the two dashboards show only their own visits.