Goodness, that's a bit frustrating!
Before reaching out, can you please double check you've allowed permissions for the Plann App to send you notifications?
How? On your phone, visit:
Settings > App Permissions > Plann
and make sure we're allowed.
Additionally, if you’re really low on battery, some devices decide to turn off notifications in order to preserve your battery life which can mean you might miss your Plann post notification.
For more information about how to manage notifications on your Apple devices, please visit Apple's support page.
For more information about how to manage notifications on your Android devices, please visit Google's support page.