I Have a CAPsMAN with 9 CAP devices on it. Al those CAPs have the same configuration: 4 SSIDs, 2 of them can access the local network (same bridge as the local network) and the other 2 SSIDs don't have (separate bridge, named guest-bridge). The problem is:

I Have a wireless sound device connected to a determined CAP, and I should be able to manage this sound device by my cellphone. And it works, unless I connect my cellphone to the same CAP that the sound device is already connected. I cannot even ping the sound device. When I walk away to force my cellphone to connect to any other CAP, it back works. I never saw this behavior considering that the CAPs are all on the same bridge, and I can continue ping other devices and even continue with internet access.

Assuming you're running legacy capsman (with separate configuration subtree under /capsman) ... your caps-man datapath config most probably lacks setting client-to-client-forwarding=yes ...