We recently changed the design of an email that goes out every month to 70 000 subscribers. (Switched from a regular single-table HTML to spongy/hybrid MJML-based markup.) After the change the open rate of this email dropped from average 48% to 22% and I'm looking for possible reasons. Does anyone have a possible explanation for that - I'm wondering if the new layout could have caused that, or the reason is something else?
I'm seeing one other change that has happened and I'm wondering if that could be a clue: in the Email Insights view by device type, we used to have the majority of "Open" events under the "Other" platform. Now, we have way less opens in the "Other" category, but more in "Desktop". Is it possible that the open event tracking has changed?
P.S. I suspected that something caused the email to land in the "Promotions" tab or spam, but that wasn't the case as our tests show.