Cracks and, even more so, warped/buckled hulls. I've owned 2 riveted hulls, a Mirrocraft and a Lund. If you look at some manufacturing videos between different aluminum manufacturers, you'll see the stringer systems in both of those riveted brands are far superior than any welded brand, at least, that I've seen. The stringer systems dissipate energy thru ought the entire hull. Lund also uses a double plated bow to absorb wave impact.
The above being said, If you are using the boat on water that rarely sees anything above a 2ft chop, it's probably not a big deal. If you frequently fish larger rougher bodies of water, there might be better options.
Going to correct you sir. The Lund is more of a hybrid hull. Deep V in the bow and pad in the stern.