The error type 3 is easy. Your GND net doesn’t have a power output pin anywhere on it. You need a power flag (PWR_FLAG) on that net as well. More details can be found at this FAQ item:
As to the error type 12… I don’t think that I’ve seen that one before. Hopefully someone else may have an answer to that one. Since the U1 isn’t U1A, I’m not sure how “another unit of the same component” applies here…
BTW, there are several versions of KiCAD currently being used out in the wild, each with their own quirks. Please inform us which version you are using so we know which quirks apply.
Is it possible you have another symbol in the same schematic that uses the U1A reference? Maybe kicad is just confused because it finds the same reference twice. You could run reannotation with “delete old annotation” selected.
Ok, now I am 99% sure, someone has taken the 4 pin symbol and adapted it for the 3 pin DRV503 by changing pin 4 to GND but not deleting pin 3 NC. Replicating these steps I get the same error: