In iOS 14, you may notice that the interface for snoozing reminders from notifications can become empty/blank. This usually happens after Due is updated from the App Store (whether automatically or manually). This is a bug in iOS 14, which we've filed a report with Apple (FB8715315 - Notification Extension Frequently Not Loaded in iOS 14). To resolve the issue, please restart your device.
Update 10 May, 2021: Apple seems to have mitigated this issue as of iOS 14.5. You may not encounter this problem on iOS 14.5 or later, if you are updating from Due 21.4 to later versions of Due.