With a phone (Nexus 4) connected, going into 'Internal Storage', everything seems to be working properly. But then whenever i click on a folder in the Folder Tree, the main file display is returned to the root, and only displays the top 'folder' called Internal Storage. So I'm back at the beginning. I can only truly navigate anywhere through the main file display, and back the way i came. Can't acces any folders directly.
And yes it's working in Explorer.
Any ideas?
Toggling Prefs / Misc / Advanced: mtp_enable to the opposite setting to what it currently is can help with some phones.
Updating the phone can also help (or make things worse) by updating its MTP stack. But I'm guessing with a Nexus 4 it's already on the latest OS version before Google's stopped releasing updates for it.
Beyond that, I don't really have any ideas. I avoid MTP as it tends not to be very reliable (even if you use vanilla Explorer; there are major issues in both the Android and Windows sides of the MTP stack, as well as design issues like it only allowing one thing to access the device a ta time). Installing an FTP or SFTP server on the phone works much better, and lets you use the FTP client built into Opus. It also works wirelessly. The only downside is it is slower (wifi vs USB speeds), but not that much slower, so it depends how much data you are transferring. (For me, it's quicker to use FTP than it is to plug in the USB cable and wait for the phone to switch to MTP mode, but I don't transfer huge files to my phone often.)
I see. I didn't know FTP was an option. And sometimes i just like to connect a wire and it's done. Haven't had problems with reliability that i know of. It just connected, i clean it up, and i disconnect.
Isn't MTP like a standard that should work the same anywhere, like USB for example? Didn't think that the phone's OS would matter as i thought MTP would just be standard. But i'm using LineageOS actually. So it's not native, but it is very recent. 5 days old now the latest version with Android 7.1.2. The previous one a month ago, and both have the same problem.
So i tested a Samsung Tab S2 just now (on Android 7.0) and it's the same problem. Selecting any folder in the Folder Tree just reverts it back to the beginning like this:
Oh and indeed i tried setting mtp_enable to false, and that makes the issue go away. Which is great. But i don't know if turning it off is really a proper solution though. 
Are there any pros or cons to using or not using Opus' native MTP support?
There must be a reason it's there, and on by default.
Edit (again): Actually it's the reverse now. Now it's double clicking a folder in the main window that does nothing. I can only get into folders using the Folder Tree. 
Also i found the downside to non-native MTP. Can't change the view using Opus' interface, only via right click. And no custom background color etc. (or any other Opus features probably?)
MTP is standard, but a very limited one (for things that want to do file management) that has also been poorly implemented in both Windows and Android (although it's possible it has improved, or will improve in the future). Implementation quality also varies with 3rd party versions of Android.
A bit like WebDav is a standard, but using it in Windows has usually been guaranteed to be a pain.
As an example, I used to run into issues where the phone would stop processing MTP requests until it was rebooted.
Turning it off is fine if it works better. It just means more things are routed through Windows than through our own code, which some phones like better (and some like worse). (The low-level MTP protocol is always handled by Windows. The switch just changes how Opus talks to MTP at the high level.)
