Suddenly site traffic (mostly) not being tracked (since update?)

Matomo worked now nearly perfect. Suddenly on 7. Oct most site traffic is not being tracked. I lost >50% of all traffic. 90% are iOS users. Google Analytics show the correct number.

Not sure if this is realted to the last update?

This is my tracking code, which is implemented in head area of my WP site.

<!-- Matomo -->
  var _paq = window._paq = window._paq || [];
  /* tracker methods like "setCustomDimension" should be called before "trackPageView" */
  (function() {
    var u="//";
    _paq.push(['setTrackerUrl', u+'matomo.php']);
    _paq.push(['setSiteId', '1']);
    var d=document, g=d.createElement('script'), s=d.getElementsByTagName('script')[0];
    g.async=true; g.src=u+'matomo.js'; s.parentNode.insertBefore(g,s);
<!-- End Matomo Code -->

Do you mean 90% of your looses are iOS, or in general your traffic is 90% iOS, of after the drop 90% of users are iOS?

Also, can you check if there is something in the error log file?