Many times. OpenWRT is the most prominent example. Apart from SFC, in Germany, Harald Welte at gpl-violations.org was enforcing the GPL too for several years.

Many times. OpenWRT is the most prominent example. Apart from SFC, in Germany, Harald Welte at gpl-violations.org was enforcing the GPL too for several years. https://gpl-violations.org/ https://gpl-violations.org/