More than likely this is caused by your site being in Staging status. Staging status does not always display everything 100% as it does live. To check if your site is in Staging status navigate to:

onMessage > Website > Stie Name > Site Settings > Current Status
If Staging is Selected, the staging URL will be in the following format: SITENAME.SCHOOLNAME.onmessagestaging.com
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Once you make your Site Live, the issue will no longer occur.