This has been going on for years but I am finally posting since we are totally stuck this year.
We collect a lot of photos. Every year just after the service hits 10GB the Export to GDB starts to fail.

It will sit like this Exporting for hours. Then the Export button goes back to not greyed out and clickable again.

The resulting file that is created is way smaller than it should be.

Been trying for weeks.
This is also happening in my nightly backup script. It fails on this line every night.
fsLink = gis.content.get(itemId)
result = fsLink.export("tempOut"+ HFSname, "File Geodatabase")
raise Exception("Could not export item: %s" % self.itemid)
Exception: Could not export item: 713e3aaef9674e34555555333b618
It fails in arcgis.gis here
if wait == True:
status = "partial"
while status != "completed":
status = export_item.status(job_id=res["jobId"], job_type="export")
if status["status"] == "failed":
raise Exception("Could not export item: %s" % self.itemid)
And again it leaves a export file in AGOL that is way too small.
Last year I could get some to download over 10 GB but pretty rare. I also tried using REST in the past but that fails also once the file gets around 10 GB.
Next I took out all layers but photos and that usually works but photos are important to backup.
Most of the time now to get an export I have to make a replica and download that. Not a great option.
Why is it failing at 10GB? Does it have something to do with a AGOL limit - I think photos used to be 10GB.
We really need a nightly backup, and since none is available in AGOL strangely this is the only option.
Appreciate any input. thanks!