Why are my participants' checkmark progress not showing up properly when they view their rewards?

When a participant has fulfilled the required number of referrals to earn the reward, the checkmarks reset and an indicator that the reward was earned will be displayed in the upper right-hand corner.  In the example figure below, the participant has previously earned three rewards total - as indicated by the encircled +3.

The total number of checkmarks represents a participant's threshold to reward achievement(s). 

When a reward requires multiple referrals to unlock, checkmarks are "filled in" to visually represent a participant's progress with grayed checkmarks representing non-existent or unapproved referrals. 

Note: If your campaign's reward is unlimited (can be earned multiple times) and the reward threshold is 1 referral, the checkmark icon will always remain grayed as displayed in the image below.

In the participants' view, the +1 will represent an earned reward and a little red dot will appear within the GrowSurf window denoting that there is a newly-earned reward.