I have not seen anything so far when searching.  Maybe suggest opening a ticket with Support as there could be a registry key that they can give you to help with this that is not public. 

I had already opened a ticket with the very slow Veeam support.

They finaly answered, and the solution was to run a active full backup copy, because the active backup chain on the Storefront consisted of more than 192 restore points. 

Thanks for getting back with the answer to your problem. I didn’t have that in mind, but there are limitations regarding the length of the backup chain; so you should regularly do active or synthentic fulls (active prefered): https://helpcenter.veeam.com/docs/backup/vsphere/deduplicating_appliance_storeonce.html?ver=110#limitations-for-hpe-storeonce

In an enterprise environment, are these limits easy to reach or are they extreme cases?

I think a backup chain with 192 restore points and more is rather extreme….

The backup chain is reset with every active or synthetic full.

Thanks @JMeixner , I was hoping for a similar response.

Glad to hear you got a resolution never thought about the chain length.

In addition to @JMeixner ‘s answer, you should always configure a full backup when using a StoreOnce as a backup target; endless incremental won't work.

@kitt Which model do you have in place?

We have a StoreOnce 3640.

All our jobs is configured as forever incremental  with syntethetic full backups every week.

This have been working a long time, but something must have happened since this error came on a lot of backup copy jobs now. 

If the chain is increaased by one for every incremental backup we should have 42 after a week, or 192 after about 4,5 weeks. I havent had time to investigate this, but I can not belive the fulls have not ran for over a month. 

Maybe an Active Full once a month will help too and ensure it won’t happen again.