We apologize for the instability of composr.app and appreciate your patience. We are working on the statistics addon and trying to find an optimal way to store and render data. Unfortunately, we have yet to find a solution that can handle the traffic (and therefore, tens of millions of statistical records) of composr.app. We're working hard on one.
#2268 - Composr 10b3: Failed query when trying to send a newsletter
Workaround:
Please delete the newsletter_drip_send.d_message__text_parsed and newsletter_drip_send.d_message__source_user fields from the database.