Dear Julie,
the most likely reason is that the code-set was set for "multiple user" (double) coding when the "now disappeared" coding was applied. It was then moved to "single user" mode, but without completing the coding for some or all items. If you'll look at the review-statistics tab (bottom right of the main screen), you'll find the exact numbers that apply to your specific case (look in particular at the "Incomplete coding" box).
There are two ways to proceed now, which one is best depends on how items were allocated amongst the team members:
If each single reference was allocated to one and only one reviewer, then you can use the review statistics tab to complete the coding for all items in just a few clicks. In "review statistics", "Incomplete coding" box, expand the appropriate Code-set and click on the green V for each reviewer, this will mark their coding as complete. The end result will be equivalent to what would have happened if the the code-set was never configured for "multiple user", which is the correct option for this (one reviewer per reference) type of scenario.
If each single reference was allocated to more than one user, then you should revert the code set to multiple-user data entry and proceed in the usual "double coding" way (create comparisons, complete agreements, evaluate and complete each single disagreement), please see the double coding video for details.
If you are in a "mixed" situation, where some references have been coded by two people, and some by one only, then the situation may require some more attention, please let us know if that's the case.
I hope this helps,
Sergio