Since I started using Android, I have tried many things to find a reliable file copy from or to my device. For a single file copy, the default mode using USB is slow but kind of works. But in case you need to copy 400+ files with several gigabytes, this takes ages and some files will just not be copied without any message.
I also tried several “File Transfer” apps from the play store, they all were either fast, but unreliable, or slow and unreliable or just plain broken. So I searched for something different and the final solution was using FTP (File Transfer Protocol).
Start the FTP Server, tap on “Login settings...” and change the default user and password to something unique for the sake to security. Please do NOT activate anonymous login, again for security reasons.
Go back to the main screen of FTP Server and flip the ON/OFF switch on ON. It will now tell which IP address and port it is using. Please make sure that your Android and your computer are connected to the same network so the connection will work.
Launch FileZilla and enter the data from the FTP Server in input fields below the toolbar. In Host: enter the IP Address from your device, in Username/Password the entries from “Login settings...” and in Port 2121 (default setting in FTP Server). When done, click Quickconnect.
FileZilla should now be able to connect and show you the contents of /sdcard or /storage in the right section. The contents of your PC are on the left, so you can simply drag & drop items between your PC and your device. Once you are finished, open FTP Server again and set it to OFF.
If you need access again, turn FTP Server ON, start FileZilla and select the dropdown field behind Quickconnect to open the connection again.