SUMMARY
Can't copy or move files from a SMB to an USB storage device. Issue is not persistent but happens most of the time. Doesn't seem to make a difference whether it's an USB stick or a smart device, but I'm mostly trying to copy to smartphone or tablet so that's where I'm noticing it the most.


STEPS TO REPRODUCE (not always reproducible)
1. Navigate to SMB storage with dolphin ("smb://some_nas/some_folder/")
2. Select a file or folder and copy or cut it to the clipboard
3. Navigate to USB storage device ("mtp://some_device/disk/some_folder")
4. Paste file or folder from clipboard

OBSERVED RESULT
Status window: prepare copy/moving with bouncing progress bar
If you refresh dolphin during that time it shows empty directory
Error message: "Could not write file" (it seems to depend on the file size how long it takes until the error message appears)
Dolphin needs to be refreshed and it takes very long
Mostly file is created on USB device (and then always less than 50 bytes written)
Sometimes the connection is lost and sometimes it won't even recover until reconnecting physically

EXPECTED RESULT
Status window: copying/moving with advancing progress bar
File copied/moved to USB device (dolphin refreshes automatically)

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Ubuntu 22.04.2 LTS
(available in About System)
KDE Plasma Version: 5.24.7
KDE Frameworks Version: 5.92.0
Qt Version: 5.15.3

ADDITIONAL INFORMATION
Copying the same files from SMB to local and then from local to USB always worked for me.
Never noticed any problems copying/moving files from USB device to SMB or from SMB to SMB.