This could also be due to data uploads being mapped to the wrong properties during the upload process or due to incorrect properties being used in the forms.
Double-check your forms and what properties they're mapped to on the platform. To do this follow these simple steps.
Here we have the input label changed to "Mobile telephone number".
Open the form edit window by hovering over the form and clicking the green edit icon. Then click edit on the field you need to check, in the example, it's the "Mobile Number".
But it's actually mapped to the "Last Name" property on the platform.
This would occur if someone has selected any property and renames it. It is vital not to do this. You can make subtle wording changes e.g mobile telephone number, but not complete property changes which would mean the data no longer makes sense e.g last name.
Always ensure the property is appropriately selected.