Have you created a Product with more than 50 devices under it? If you use the UI to verify that devices have been created, you may notice some strange behavior once you pass this threshold.
If you take a look at our Device Service API you may notice that the Device.list() function returns 50 devices by default. Currently, our UI emulates this in order to display the devices under a Product, thus leaving some devices without a place in the interface. Rest assured, if you are using a valid process to create your devices, they are in fact being created and do exist in the system for use, this is a bug that affects only the UI. To verify that all of your devices have been created, use the API directly and specify a limit beyond the default 50.
Of course if you have any questions or run into any trouble, do not hesitate to contact Exosite Support at: https://support.exosite.com/hc/en-us/requests/new