@User: The gating factor is the number of items in a symmetric partition. So 1774 symmetries likely means that each symmetric partition had only a few components in it, so it was very fast. "2 symmetries" means that it could have lots and lots of components in the same partition, which is what causes trouble. In particular, it is the standard cell designs with lots of fill cells that do this. In some cases (plain fill) netgen can just be told to ignore the fill cells. For one of the openlane antenna violation handling methods, lots of antenna cells are dropped into the design like fill. Since some of these get connected, they cannot be ignored, and so they will end up as symmetric partitions. Same for tap cells.