Recently, we have seen an increase in the number of jobs failing with the error message: Object reference not set to an instance of an object.
Typically, when a large number of jobs start failing with the same error messages it indicates a backend change from Microsoft is the cause. We’ve opened a Veeam support case to identify a solution to these issues. Veeam support identified the issue as recently discovered and currently being reviewed by the R&D team.
In the meantime, a workaround that has worked for us is to edit the backup job to increase the number of retries on jobs encountering this issue. The issue seems to be sporadic, so by increasing the retries the Veeam job will still fail with warnings but then automatically retry for the specified number of retries or until it is successful.
For more information on increasing the retries see the Veeam documentation here:https://helpcenter.veeam.com/docs/vbo365/guide/specify_scheduling_options.html?ver=70
Source: https://www.managecast.com/veeam-for-microsoft-365-object-reference-not-set-to-an-instance-of-an-object/