Issue / Fault definition
You get a black bar at the bottom of your extended screen when using multiple monitors.
Known / associated error messages
Known Fixes / Solutions
To fix the issue simply switch from Extended mode to PC Screen only using the Windows Key + P key combination then back to extended mode once again.
This looks to be a drive issue and will hopefully be fixed in a later release pulled down via Windows Update.
Ensure all devices are up to date with security and vulnerability patches from Microsoft and third parties.