Are you using a Samsung phone? If so then it is due to a problem with the MTP specification and Samsung's crappy implementation of MTP.
tl;dr version: never open a Samsung phone through the device notifier or whatever hardware mounter your DE uses. Always open it from within the file manager you want to work with it in. And never open more than one window or more than one application.
Basically, the problem is that, unlike UMS, MTP doesn't allow more than one connection to the same device. What happens if you click on the phone in the device notifier is that plasma closes it connection and hands it off to Dolphin, which then opens another connection. On Nexus devices and many others this works fine, they just close the old connection and create a new one on the phone end as well. But with Samsung devices the phone chokes when this happens, it can't break the connection and establish a new one while it is still connected to the computer.
The trick is to always open the phone from within dolphin (or whatever your file manager is), and keep the same window open as long as you are working with the phone. Do not try to access your phone from another window or application. If you close the file manager then you have to unplug your phone and plug it in again before you can access it again.
Similar problems can, unfortunately, also happen during long file transfers. This is harder to work around, but luckily MTP is transactional so you shouldn't get partially-complete files.
The developers are working on a solution to this problem, but they want to do a lower-level fix for the problem (have one system-wide connection) that every project can share rather than a KDE-specific solution that leaves things broken for everyone.
You can read more about it here: http://philipp.schmidt-rheinhausen.d...-with-kio-mtp/
tl;dr version: never open a Samsung phone through the device notifier or whatever hardware mounter your DE uses. Always open it from within the file manager you want to work with it in. And never open more than one window or more than one application.
Basically, the problem is that, unlike UMS, MTP doesn't allow more than one connection to the same device. What happens if you click on the phone in the device notifier is that plasma closes it connection and hands it off to Dolphin, which then opens another connection. On Nexus devices and many others this works fine, they just close the old connection and create a new one on the phone end as well. But with Samsung devices the phone chokes when this happens, it can't break the connection and establish a new one while it is still connected to the computer.
The trick is to always open the phone from within dolphin (or whatever your file manager is), and keep the same window open as long as you are working with the phone. Do not try to access your phone from another window or application. If you close the file manager then you have to unplug your phone and plug it in again before you can access it again.
Similar problems can, unfortunately, also happen during long file transfers. This is harder to work around, but luckily MTP is transactional so you shouldn't get partially-complete files.
The developers are working on a solution to this problem, but they want to do a lower-level fix for the problem (have one system-wide connection) that every project can share rather than a KDE-specific solution that leaves things broken for everyone.
You can read more about it here: http://philipp.schmidt-rheinhausen.d...-with-kio-mtp/
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