Thanks for your help. The game in question is Kingdoms of Amalur: Reckoning (the original version, not the remaster). I tried various versions of ways of inputting the coordinates. Using the link you gave, I tried adding a command to briefly move the mouse before executing the rest of the commands. So the sequence is now:
Move mouse left 1 relative mickeys from cursor position
Save current mouse location
Move cursor to screen coordinates (939, 389)
Click left mouse button
Recall saved mouse location
Whether or not I include the first line or the two cursor save and recall lines, the result is the same: after executing the command, the camera goes into a wild 360° spinning. From then on, the camera no longer properly tracks the mouse.