Thank you for contacting us. If mSecure apps on different devices are signed in to the same account, the change of the username on one device will be synced over to the app on other devices. It sounds like you have two accounts here. Real quick, can you let me know the two emails you see in the Account Settings of mSecure on both devices?
Thank you for the update on your situation. Are you now signed in to your "firstname.lastname@example.org" account on your laptop, and if so, do you see all your information in mSecure on that device?