The original allegations against the UNWRA were unsubstantiated by any evidence, and the last two times they found tunnels there has been suspicion cast on the authenticity of the finds due to signs of tampering and misinformation by IDF forces. Its hard to lend much credence to their third time claims about an “electrical supply room” tunnel.
Nor would any of that justify ~30,000 mostly women and children even if it were all true.