Looks like the key servers are useless, and the FreePBX key has been poisoned (evidenced by the failures).
So as I understand it, module signature checking can only happen against signatures that are local on the PBX. And those could get corrupted if someone gets access to your PBX via exploit, making signature checking useless.
Seems like there’s a serious problem here. Is the only mitigation at this time to disable signature checking?