I guess I've been really lucky. Triacs yes, SCRs/SSRs no, never had one fail in either the open or closed position. But then I've used only
ETC/LMI dimmers since about 1990. There, I finally said something nice about ETC! Never replaced an
SCR on a Ward-Leonard or Kliegl
dimmer either. I may have on a very early CD-80 pack though, now that I think about it.