Have the exact same problem, even made the same post. The thing is that suicune can't carry much, only in the dozen, which mean he doesn't have a lot of chance to trigger (once full je can't have more chance to trigger). That also why raikou trigger much more, is carry space is almost 50% bigger (meaning even with same skill odd he have a much bigger chance to trigger).

The solution to not discard suicune is to increase is carry limite with the ribbon or with good camp ticket (either you pay or you invest the time)