Andres, I guess the switches are not in production, so in case if you can change the configuration and reboot the switch at will then i would suggest to isolate the issue with below steps. remove the ports 9,10 from all the VLAN's loop back the ports 9 and 10 using the same cable used in port 9 or port 10. reboot the switch and see if the ports are flapping. Try the same on the Telecom equipment. This could give a fair idea where the issue is. I would get back if i find any such case is recorded before.