I am sorry to hear that you are not having the open rate success that you are used to seeing. I did take a look over your campaign, and I believe it is a great email. Having images and links usually helps with open rates, because they help engage your readers.
The reason you may have seen a few people on the Did Not Open list, is due to the fact not all opens are tracked. In email clients like Outlook, where a reader can preview the email on side pane, it will not track as an open unless they click on the email name and it pulls up as a full window.
To help with your open rates going forward, you may want to look into using different effective subject lines, or looking at these tips for getting more contacts to open an email.
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