Full and Incremental backup size issues and discrepancies.

As the title briefly mentions my organization and myself are having issues with Netvault, ESXi and the size variances of full and incremental backups. I'm currently backing up 7 VMs with a total of ~5 TB of allocated space. Our full backups have consistently been ~4.6 TB in size which isn't a major discrepancy. I figured it was backing up actual data or compressing something. However, the last full backup to complete was 3.18 TB in size. The logs do not show any failures or issues. VM sizes have not changed.

For several weeks the incremental backups have also been ~4.6 TB in size. Which is obviously an issue. We're basically doing full backups daily. This wouldn't be a major issue but all of these backups are now taking 10+ hours to complete. Just this past week all of the incremental backups are between 150-200 GB in size. Indicating that the incremental backups may be working properly now. My concern is that all of these changes and discrepancies have happened when nothing has been changed on my end. The jobs have just been running while I continue to research ways to fix our issues.

Any suggestions or starting places would be great. I will try and provide as much info as I can. I will also admit I am still learning about backup solutions, but I am NOT the initial creator of these jobs nor have I modified these jobs in a way that may have caused this. The issues have been present prior to my involvement, but I am the one trying to find solutions. Thank you