Hi patricksgolden,
Thank you for posting in Apple Support Communities. We can definitely understand needing to log into your Starbucks app. Does this only happen when you are connected to your Wi-Fi network or does it happen on your cellular network as well? You tagged an iPhone 12 Pro in your post, is it running the latest iOS ( 14.4.2 is the latest currently)? You can check for an update by going to Settings > General > Software Update. If needed, be sure to back up your data before installing it.
Since following the steps from the app support team, has the app been closed out and relaunched? Check out how to do so here: Close an app on your iPhone or iPod touch
Here are some other article that may help:
If an app on your iPhone or iPad stops responding, closes unexpectedly, or won’t open
How to back up your iPhone, iPad, and iPod touch
Update your iPhone, iPad, or iPod touch
Hope that helps!