If you SSH into them since ICMP works, you can run some commands to try to understand why they are not showing up online in your HM instance.
I'd start with:
show capwap client
It's going to tell you the current state of the CAPWAP tunnel between the AP and its respective HM. Assuming that shows no connected server, can the APs ping out to the world? Is the VLAN they live on working internal to your LAN, but not external of your network? If not, a traceroute out to a public IP might reveal where things are falling apart.
