In non-incremental global net placement, unfixed global net assignments are discarded. In particular, all quadrant global regions that were produced during a previous execution of layout are deleted. Such automatically-generated quadrant global regions have names that begin with the prefix “Qclock_auto_”.
Action
Select the incremental placement option if you intend to preserve global assignments produced by automatic global placement. In addition, avoid naming your regions with the prefix “Qclock_auto_.”