Why Can't I See Some Of My Company's Locations On My Mobile App?

It's likely that your SiteDocs administrator has not assigned you to those locations from the Admin Panel. You will only see Locations that you are assigned to.

Contact your company's SiteDocs administrator and ask them to assign you to the Locations you need to sign forms under, then tap the Sync button on your Home Tab on your app and click the blue Sync button to pull that information down onto your device.