Add bend at the elbow and knee.
If the bones are all in a straight line in the arm or leg the IK gets confused about which way to bend.
Add the bend in edit mode. It only needs to be a small amount.
I think you probably have dependency loops. I think that the IK targets depend on the bones in the IK in some fashion, probably through parenting. Can’t have that.
If on Windows, Window->Toggle System Console to get dependency loop (“dependency cycles”) warnings.