Hello
Netlogin configuration is exactly the same as the link you shared and works perfect for all devices connected (C5 not).
I'm sure BPDU is not part of this issue. I tested BPDU executing command:
configure stpd ports link-type edge edge-safeguard enable bpdu-restrict
And port was disabled. I restored original config.
Maybe configuring LLDP to advertise C5 MAC info can help. I will test.
Thanks