Backend Events Missing Associated Frontend Events

We use Snowplow in conjunction with our feature experimentation system, and we track experiments on the backend before the page is served to the user.

Therefore, when a user visits a page with an experiment, we should presumably receive both a backend experiment event and a frontend pageview event shortly thereafter.

However, we’re noticing that for a very significant number of backend experiment events, we are not receiving any frontend events associated with that backend event’s domain_userid.

We’re aware of a few reasons this could be happening: people leaving before the page loads, browsers blocking JavaScript, extensions blocking calls to Snowplow, etc.

However, we don’t think these alone can fully explain just how many single-event domain_userids we’re finding.

Are there any other possible explanations we might be missing?