It's the failure of the Lebanese government to impose the rule of law and maintain the security and stability of the country, including the Palestinian refugee camps. Though Lebanon never misses an opportunity to condemn Israel, Palestinians in Lebanon are treated like second-class citizens. Mostly, it's the failure of the UNRWA that only exists because of the international community's commitment to propagate Palestinian political fantasies.
When the camp was established, it was only intended to offer a temporary solution, not to last for 56 years. Though Palestinians are deeply discriminated against in Lebanon, ultimately the only reason for their presence in the country is because of Israeli ethnic cleansing in 1948. Indeed, at times, international aid inadvertently compliments Israel's colonial policies toward Palestinians as it prepares to annex even more Palestinian land in the West Bank.