[Verizon LG G4] DrRichardQuack:
IMPORTANT UPDATE:

So, I just removed the Exchange email account that enforces full-phone encryption, and formatted the external SD card, and now copying to it works perfectly fine! WTF! Isn't copying to the external SD card supposed to work even if the external SD card is encrypted???

ORIGINAL POST:

At some point in the recent past, the ability to copy files to my phone's external SD card ceased.

I will preface this post with the fact that I have two external SD cards:

1.) 32GB card that LG provided with the phone (via the rebate offer that included the 32GB SD card, the spare battery, and the charging cradle).

2.) 64GB SanDisk Ultra that I bought separately.

The 64GB card worked fine when I first bought it, which was shortly after buying the phone.

As time went on, I began seeing errors to the effect of "SD card unmounted unexpectedly". This occurred most commonly when browsing the songs on the SD card in a media player, for example.

I'm not sure if this started before or after I began encrypting the contents of the external SD card (my work's Exchange server began enforcing encryption of all storage on the phone).

When I grew sufficiently tired of the unexpected unmounting behavior to retire the 64GB card and try the 32GB card, I was somewhat surprised to find that the 32GB card is fine and never unmounts unexpectedly.

I thought, "Well, at least the problem is solved. Maybe the 64GB card is bad and I'll mail it to SanDisk for a replacement." Wrong.

While the unmounting no longer occurs (maybe the 64GB card really is bad), I can no longer copy files from my computer (or any other computer that I've tried) to the phone's external SD card.

I have tried with both the old/broken 64GB card and the 32GB that still seems to work fine in all other scenarios. Both cards exhibit the exact same behavior, which makes me think that the inability to copy files to the phone's external SD card through the included USB cable is unrelated.

I have tried from Windows 7 and Windows 10, with both SD cards, and I've repeatedly tried formatting both cards (while inserted into the phone). The result is always one of two things:

1.) Cannot copy [file name] The device has either stopped responding or has been disconnected. -> Stop copying -> Skip this file

2.) The copy dialog appears, and the progress bar begins to move, but it stops either immediately or about 5% of the way through (no matter how many files I'm attempting to copy of how large they are), and it hangs for 5-10 minutes, before it finally times-out and asks me if I want to skip the file or try again. If I try again, the behavior is exactly the same.

I even tried connecting my phone to a Mac laptop running the latest version of Mac OS, installed the driver package from LG, and when I open Android Transfer, the dialog tells me to connect my phone, even when it's already connected. Disconnecting and reconnecting the USB cable changes nothing.

For whatever it's worth:

1.) I'm able to copy files to the internal SD card with no problems whatsoever on the Windows 10 machine.

2.) I'm able to move/copy files from the internal SD card to the external SD card, but only if I use LG's built-in File Manager application. I suppose this is to be expected in Android 6.0 because non-system apps, such as FX File Explorer, lack permission to write to the external SD card.

3.) If I try to drag a file from the internal SD card to the external SD card from within Windows, a "Copying..." dialog appears, but it says, "Waiting: VS986 is busy." and it hangs indefinitely, until I click "Cancel".

4.) Enabling USB debugging doesn't change the behavior.

5.) It seems like the first time I connect the phone to a given USB port on the computer, Android prompts me to allow the computer to access the phone's storage. Whenever prompted, I always click "ALLOW", as pictured in the attached screenshot.

6.) I'm trying this in MTP mode, as that is the only mode in which my external SD card shows-up within the "VS986" device that is mounted in Windows when the phone is connected and unlocked.

7.) I'm using the original LG USB cable that came with the phone.

8.) I've tried all different USB ports; it doesn't make any difference which one I use.

9.) I'm able to copy files from the phone's external SD card to the computer without issue. (Well, "without issue" is an overstatement, but it works most of the time.)

10.) Software vitals are attached in screenshot.

What the hell is going on with this phone? I just performed a factory reset, to ensure that I'm starting with a "clean slate", and it didn't change the behavior.

As a final point of note, I have not tried copying to the phone's external SD card before encrypting it. I will try that and post back (as big of a pain in the ass as it is).

Thanks for any insight here; I'm about to throw this thing off a pier and file an insurance claim.