One thing I can see is that neither of the devices send a SUBSCRIBE with line-seize Event. They rather just subscribe to the call-info event, and in the oubound INVITE, they don't send a Call-Info header either. Is this mandatory for the SCA module to work?
It sounds like they're not configured for SCA properly.
Can I send you a pcap in private?
Please do, and I can confirm from the signaling whether or not the sets are properly configured.
-- Jorj