I had a customer with almost the exact opposite
We have a couple of graphic designer/artist/musician types as clients. They're brilliant in their fields, but as far as computers go, they require that their computers be, to quote one of them, "blonde proof".
Last year, one of them had their external USB backup disk die on them. So, they got a shiny new 4TB MyBook as a replacement, and they said things were good.
A few months later, things were less good. Their C: drive was starting to die, making hideous belt sander noises, and losing critical files. But when they tried to back up to the USB disk, it was out of space. Panic ensued, as the primary disk wasn't backed up, and the backup disk had no space.
I had them send me screenshots, but the external disk was 4TB, had 3.98TB free, and they seemed to be able to copy some files over, but only about 1% of them.
So, I went over and checked it. My first assumption was that it was formatted as FAT32, and any files over 4GB wouldn't fit. Nope, that wasn't it.
I had her show me exactly what she did, so I could see if it was a PEBCAK error, as it usually was.
She double clicked on the icon of the USB disk, which opened a Windows Explorer window, as excepted. She then dragged a folder from her desktop to it. And sure enough, an "insufficient space" error, with a Windows error code number appeared.
She, of course, was panicking that she was going to lose years of work, and rightly so. I tried various things, but there was no issue. I put the external USB on my laptop, and there was no problem writing to it. The disk wasn't write protected, it didn't need administrator rights, it wasn't FAT32, and in fact it could copy about 300MB of files because it gave the "insufficient space" error. What the hell was it?
So, I researched the Windows error number. Strangely, it was not a file system error, it was a OneDrive error code. WTF? She wasn't even using OneDrive. Or was she?
Sure enough, OneDrive was enabled. She hadn't configured it; she had no idea what OneDrive even was. This was one of those "it came that way when I bought it" things. Either the box store had configured Windows for her, or it was done when she set up Windows the first time. Since she was a "click yes to everything" type user, it would be whatever Microsoft sets as defaults.
In the end, it turned out to be one of the more malicious things Microsoft has done. When OneDrive is enabled in Windows 10, when you copy from one drive to another using Windows Explorers, it backs up the destination disk on OneDrive. It's totally seamless and transparent.
Of course, if there isn't space on OneDrive, the copy is aborted. And that also aborts the local copy to the USB disk, too.
Yes, that's right. Her backup was failing because she was trying to back up about 2TB of data to a 4TB disk, but OneDrive only had 5GB or so, so Windows would only allow her to copy 5GB to the disk.
This idiocy could be bypassed by using the command line, or a third party tool, or another file manager, but this was her workflow.
By logging her out of OneDrive, and disabling, and then removing OneDrive so it didn't restart at boot time, she was actually able to use her 4TB disk.
Another "improvement" that makes things worse.