As per the system restrictions, referral rewards are not credited to the users (Referrer) who share the same device with the Referee at any point (may be signed up on the same device or just logged in once on that device).
Though there could be many reasons due to which guests are not able to earn referral rewards. However, one of the major reason can be when the referrer and referee share the same device.
Please refer the image below to check the guests who share the devices:
