Jobs running to Scale-Out Repository report "No scale-out repository extents have sufficient disk space to store the backup file", while at least some of the extents have a lot of free space.
Veeam Backup Service stores information about free space on each extent in cache. When Scale-out Backup Repository resource is assigned to a certain task, number in cache is subtracted with estimated size of task and is not updated with real free space while there is at least one task going to extent. Estimates may be not precise and difference between real and cached free space may grow.
Update 2 for Veeam Backup & Replication introduces new space update logic. When extent is assigned to a new task, service cache updates free space information with the real one and subtracts it with estimated sizes of all the tasks currently going to this extent.
You can switch to new logic by creating the following registry key:
Key: HKLM\SOFTWARE\Veeam\Veeam Backup and Replication\SobrForceExtentSpaceUpdate
Default Value: 0 (Disabled)
and setting value to 1 (Enabled).
Please be aware that starting from September 2018 downloading updates will require an active contract for the corresponding product.