Will it be a problem if two devices have same device address ?? During packet forwarding will it lead to routing profile error?
No it will not, as long as both devices have a different AppKey / NwkSKey (ABP). LoRa Server stores the device-sessions using the DevEUI. When one DevAddr resolves to multiple DevEUIs, it will try to validate the MIC using the NwkSKey of each device-session.
What if two devices within the same application have same device address?
This is not recommended and you might run into issues.
@brocaar Since having same devAddr is not recommended, does OTAA activation guarantee we will always get unique DevAddr for every device?