I assume you mean urine leaking down the outside of the tube and out the tip of the penis rather than a leak in the plastic pipework outside his body.
I had a catheter for a few weeks. I didn't have RARP so not directly comparable to your husband. At one time I had a tap at the end of the catheter rather than a bag. The reason for this system is irrelevant here, but what is relevant is that when the tap was closed after a little while I would get leaking out the tip of the penis. when using a bag I never had leaking.
If your husband's leaking is just a small amount, then it is not an issue. If more is coming out his penis than going into the bag, it implies the tube is blocked and it needs further investigation.