Suppose you have a Marketing Channel processing rule like below, it should fall into the ‘Email’ channel if a page URL has ‘mid’ Query String Parameter.
However, in some cases, a page URL with ‘mid’ query parameter like the one shown below may be ignored by the ‘Email’ channel and fall into another one.
Check if the server call type is link tracking such as Custom link instead of page view. If it is a link tracking call, it is working as designed.
Adobe data collection servers strip the pageURL dimension from all link tracking image requests. As such, the page URL matching rule won’t work with link tracking calls.
Here is a little more information about pageURL’s https://experienceleague.adobe.com/docs/analytics/implementation/vars/page-vars/pageurl.html?lang=en