There are 2 possible reasons why this can happen.
1) Credits are only transferred automatically for listings after you get the Seller Wings badge. Listings that ended before you got your badge will not change when you get your badge.
2) In some cases we hold credits in the pending state due to the value of the item or high quantity of listings that are in progress. If you sell a high value item or have a large number of completed listings, your credits may be placed into a pending state.
For more details, visit: https://help.listia.com/hc/en-us/articles/203843226