Hello @JeffD09 ,
I'm not sure why the chat rep didn't perform further troubleshooting with you, but the issue stems from a glitch that can sporadically occur with certain lists upon creation. Due to the sporadic nature of the issue, the engineers are still collecting info and troubleshooting it and do not have an ETA on any hard fix.
The only workaround the devs have for it would be to recreate the list. You can do this by going into the affected list, select-all the contacts, click Actions at the top of the list > Add to list > Create new list, then name the new list to something similar. From there you can send emails to the contacts in that new list.
If your issues persist, please call our general support so they can go through all the troubleshooting processes of the issue live with you, especially to see if there's something in particular with those contacts. If you can provide the support rep with a list of the affected contacts, or have a segmentation of contacts on that list that weren't sent the email already made, it will greatly aid their troubleshooting.
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