Check and make sure that the mating of the edge is right at the very edge, with some relief behind the front of the cap iron.
Sometimes, some cap irons (without additional manipulation) just don't do a very good job of keeping the chips out.
If the knife edge fit is at the front of the cap with decent relief and the lever cap is reasonably tight and the whole assembly still doesn't work, you can experiment. However, I think given the cost of #5 planes, it's more practical to just write such a plane off and use it for coarse work with the cap iron set off of the blade a little bit.
Nearly everything can be fixed, but sometimes it's more effort than it's worth if you have an alternative.
If you have easy access to another cap iron and blade (from another plane) that fits, you can test that. It would be a good way to confirm that it's the blade and not something else.
pictures always help, too, if you want to pursue fixing the plane. (and make sure the mouth is opened up enough to avoid any issues with that - a 16th gap with the cap iron set close is preferable to ensure that there isn't a jam up adding to the problem).
One other aside - once in a while, you'll run into something with giant beam strength (larry W's word) that can just work its way under the cap in a heavy cut. Flatsawn cocobolo comes to mind - the late wood is so hard that it can go under like a putty knife slipped into a joint.