I was able to capture this scenario as it happened.
In this situation the Veeam Endpoint repository has been setup with a resource limit of 9 concurrent jobs. In the first image we can see that the backup and replication server shows EEI-NB215 is 10th in the order of jobs but it actually obtained resources as shown in the Endpoint Backup image and was able to get some of the way through a backup before having to wait for resources again.
Now, in the second image, we can see the backup and replication server shows EEI-NB215 is now 9th in order of jobs but it is still waiting halfway through the backup for the second resource assignment as shown in the Endpoint backup image. To me this means that another job after EEI-NB215 is now using available resources, since EEI-NB215 is now in the top 9 jobs and not able to proceed yet.
There must be something going on with the resource queue and how it assigns resources to the Endpoint Backups. It would be nice to have the current backup hold its resources for the entire backup process and not have to go back to the queue to get reassigned.