The 100 bonus leads continue to be earned as long as you have at least 1 upgraded 1st level referral below you.  If your bonus leads have dropped back down to 100/day, it is most likely your 1 1st level referral has canceled or their recurring billing declined.  Once once of your referrals re-activates (upgrades) or you bring in a new referral, you will once again get 200 leads/day.