Sorry to hear you are having trouble.
If at all possible, this would be best resolved if your client could participate in the thread directly.
Has this ever worked or no, icons have never properly displayed on the 2nd monitor?
If it has worked, what has changed (new monitor, new connection type, multi-monitor software installed (Ultramon, Display Fusion, Nvidia Surround))?
How is the 2nd monitor connected - is it part of a docking station - connected to a laptop or no, directly connected via - HDMI, Displayport, other - to a desktop?
When this happens, does a restart of Windows Explorer resolve the issue:
Does a purge, reinstall, restore snapshot work to resolve it:
Stardock Support Manager