Hello Resourceful,
Do you observe similar behavior for any project (orthomosaic and DEM)? In case the problem is specific for certain dataset, please send the PDF report from that project to support@agisoft.com.
If possible, please specify the OS version that you are using, the dimensions of the DEM for upload (total size, tile size).
Upd: seems that I was able to reproduce similar problem, when trying to upload DEM with about 200k x 200k pixel dimensions. We'll investigate the problem further on our side, as we've got a way to reproduce it. Smaller DEM, as I have mentioned before, was uploaded successfully.