What can block the loading of metric counters?

Question

Google Chrome

For almost two years I have been trying to catch a bug that occurs when processing an AJAX request. It was so elusive that it did not play under any browser, no matter what device the page was viewed on. Nevertheless, about 1% of users suffered from this bug...
It turned out that the problem was that some users did not load the Yandex.Metrics counter (GoogleAnalytics did not check). So even the yaCounter variable remains empty.
Question: what can block the loading of counters?

Answer 1

Some kind of ad blocker, most likely