DO v12.0
USB connection with Samsung 7 Edge phone.
DO has always had major issues connecting to my phone. Sometimes it hangs. Sometimes I can see the directories under the root, but can't access any directories or files under them. Clicking any directory in the directory list bounced DO back to the phone's root directory. Basically, DO is useless with our mobile phones.
Windows Explorer has no issues with our phones and I have to use it whenever I need to access my phones.
12.0 is quite old now, so it's worth trying with the current update (12.6) in case it improves things.
Toggling Preferences / Miscellaneous / Advanced: mtp_enable also helps with some Samsung phones. (If set to False, it won't disable MTP support entirely; it delegates more of the MTP handling to the Windows shell. That works better with some phones, although not all.)
Updating the OS on the phone sometimes helps as well, if it isn't already on the latest version available for it.
Sorry, my typo goof.
I have version 12.6 (x64) Build 6369
ADDITIONAL: I just tried to copy from Windows Explorer (phone) to DO (computer). Operations didn't complete. Do errors or anything, it just stopped the copy. Copy from Explorer to Explorer worked error free.
I've been toggling that on /. off for ages of my Samsung Galaxy S7 Edge. I give up and use Explorer. I hope the Note 8 will be better, but.........
FTP or SFTP work great with phones if MTP isn't working well. There are several good free servers for Android which will work well with Opus, and let you transfer over wifi as a bonus. (Assuming the inconvenience of plugging in a USB cable outweighs the extra speed of USB, which will depend on the kind of things being transferred, of course.)
If Windows Explorer works though, much easier to use that.
If you're happy with Explorer. 
Most people here aren't.
What is mtp_enable?
It's the setting mentioned in the first reply above.
I get the setting. I'm wondering what "mtp" means/does? I'm trying to better understand the feature/setting.
It's a protocol used for file transfer over USB with most smartphones (other than fairly old ones).
Yeez Leo do you have to bite back all the time? That does put me off posting!
I hate Explorer as much as any DO user, but in this one area it does work better than DO does. I'm not happy at using but I have no choice.
I was explaining that you do have a choice of using FTP or SFTP, which work well (and wirelessly) without the problems seen with MTP on Samsung phones.
Only downside is slightly lower speeds with most wifi, but in most situations that's offset by the bonus of the transfer being wireless.
Okay, I'll try to be less sensitive then
Have the same problem with Galaxy S8 and S6 Samsung phones.
Been an ongoing issue.
Hangs on jpg file transfer from phone to pc
Tried changes to Enable or Disable MTP
Does not help
Running Opus 12.10 x64
Windows 10
I recommend using FTP if you're having problems with MTP. It's much more reliable, very easy to set up, and lets you transfer wirelessly.
Care to make a recommendation?
I use the FTP Server in Solid Explorer. It works flawlessly. I think someone on this board (Leo, perhaps?) mentioned it and as I was having the same issues as you on a Samsung S6 I gave it a go.
That's what I use as well (since I also use Solid as my file manager on Android, and it's built-in to the same app). But there are lots of others too. I haven't personally tried any others in a few years so I don't know which to recommend, but the Play Store reviews usually cover how well things work.