One explanation could be this:
Your referral may already have an account with another one of the Rewards casinos. Either they signed up through another affiliate, or they signed up directly (without an affiliate) in the past.
The original referrer gets ALL revenue generated by that player. It doesn’t matter if you refer them to a “different” casino within the group that they’ve never played at before.
When this happens, Rewards will “re-tag” the player and remove him from your account. That might be what you are seeing. (I can’t be 100% sure, though).
Maybe Yaniv or Renee can explain this a little better. 