In some rare scenarios, serial numbers that are attached to tax receipts can be used by the system without being connected to existing donations. This will result in tax receipts that are not generated with completely sequential serial numbers. CommunitySuite uses a low level database function that manages sequential numbers. The database software is engineered to deal with race conditions and transactions that may happen at the same time, and it will not hand out duplicate numbers. There are corner cases where these sequences may jump due to a database error or database fail over.
While there is currently no way to modify those incorrectly assigned serial numbers, our engineering team is currently looking into a different way to manage the sequential numbers to have more control, with a slight sacrifice in performance.
If affected by this issue, in the Donation Receipt report you will see rows that use a serial number but do not have an attached tax receipt.