When your iPhone StandBy screen continuously reverts to default or changes unexpectedly within a minute, it is usually caused by Smart Rotate or Widget Suggestions re-enabling themselves and overriding your custom layout.
Try this
Disable Smart Rotate and Widget Suggestions: Long-press your widget stack in StandBy mode (or edit the stack on your active home screen widgets) and turn off Smart Rotate and Widget Suggestions. When these features stay active, the system automatically cycles or restores default multi-widget lists, causing your custom configuration to vanish.
Check Lock Screen Access Permissions: Go to Settings > Face ID & Passcode, scroll down to Allow Access When Locked, and make sure Lock Screen Widgets and Live Activities are toggled ON. If locked access is restricted, StandBy cannot properly maintain interactive or custom widgets.
Toggle StandBy Off and On: Navigate to Settings > StandBy, turn the main switch Off, wait a few seconds, and toggle it back On to clear out temporary display glitches.
Perform a Force Restart: Quickly press and release the Volume Up button, quickly press and release the Volume Down button, then press and hold the Side (Power) button until the screen goes black and the Apple logo appears.