Hello Redeyedvireo,
If you haven't already, make sure your iPhone software is updated then check for updates to your apps as updating can resolve many odd issues. Be sure to back up your iPhone before updating. Here are some guides to help:
Update your iPhone, iPad, or iPod touch
How to manually update apps on your Apple device
If the behavior continues, are you able to edit the date after adding the boarding pass to the Wallet app? Also, check to make sure "Automatic Updates" is turned on so the pass can receive updates from the app (issuer). Those steps and more can be found here: Manage your passes in Wallet on iPhone
Let us know how it goes.
Take care.