iPhone - how to disable Shake for undoing read/unread email?
Open the settings app
Swipe down slightly
Enter undo in the search field
Tap “Swipe to undo”
Make your choice


The setting is global and not app specific.
Since you didn’t list actual troubleshooting steps, once you conclude you can suppress this by disabling it globally and that it returns.
Look for other differences for your experience. Different accelerometer sensitivities, different actual accelerations or pursue software resets.

power cycle it normally
force reset the device
Leave the undo off for a day globally
restore the device
swap or repair the hardware

Being organized is the only way to troubleshoot a frustrating situation like you mention.