Always when selecting "Update PCB from Schema" a component named U? is showing up. When selecting it and clicking hotkey X, I'm thrown in the Shema view, but nothing is selected. I can't find any component with the name U?
And the schema not showing the component anywhere:
Solved. Took me some time, but I was able to resolve this using
Edit -> Anotatate
Click Reset
Click Anotate with "Re-Anotate all" selected
The U? component was visible and selectable afterwards in the Schema designer and I was able to delete it. After updating the PCB from Schema, I had to re-do some of the routings, as they where missing.
Brand new interactions and interfaces. 
Easy to use and quick to get started. 
What happens when you click on U? in the Schematic Design Manager Components list?