I've only seen this on DPM 2022 when using Modern Storage, but presumably this can happen on MABS as well since they share code base and may happen on older versions of DPM.  The problem is that after some time, you will look at storage consumption metrics of various protected resources and see the consumption is being shown as 0MB.  This is concerning, of course, because does it mean you lost your backups?  Well, if you are having the same problem as me, the answer is no.  I was able to see storage valid recovery points, could restore from them, and could also see storage space being used in the storage pools.  So the issue seems to only impact queries of storage consumption, not the validity of backups, or the free space in the storage pool.

I haven't been able to find a cause or a trigger for this, I'm going to guess this is a bug that doesn't affect a huge number of users.  However, when I opened a case with Microsoft, the technician immediately knew what was happening and led me to a solution (below).  He indicated that it should permanently resolve the issue, but if not, just keep running the same command again.  It happens frequently enough for me I just decided to run this weekly in a scheduled task.

Anyway, to fix, open the DPM (or MABS) PowerShell console, and run the below PowerShell script.  It is located in the "bin" folder for the installation, so something like C:\Program Files\Microsoft System Center 2022\DPM\DPM\bin.

.\Manage-DPMDSStorageSizeUpdate.ps1 -ManageStorageInfo UpdateSizeInfo