A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC) in order to keep its time of day close to the mean solar time. Some software experiences problems when leap seconds are inserted (e.g. inserting it at an earlier date).
The previous leap second insertion, which occurred on June 30, 2015, revealed no issues with any Veeam products, and it is expected that this will be the case for the next leap second insertion.
However, this may not be true for any other infrastructure components and/or software, and it is recommended to check with third-party vendors which your company's business relies upon.