WP Rocket is a plugin used to improve the blog performances and offer a cache system. WP Rocket has a special a feature: when it finds in the URL loaded by a visitor the three Google Analytics tracking parameters (…) it serves the cached page is available ignoring ALL the URL parameters.
That creates a problem when Newsletter (but could affect other plugin) generates URLs with parameters to identify users while tracking opens and reads and the Newsletter Analytics extension is installed. The latter extension actually add your Google Analytics tracking and their recognized by WP Rocket which stops the further processing of the page. Hence Newsletter has no possibility to process the request an activate the required procedures.
To solve the problem, you should check the WP Rocket options to disable that special feature.
We’re working to mitigate the problem at least on special Newsletter URLs (for example the ones which lead the subscriber to the profile page or the cancellation request page).