Your MX will be performing NAT, so once you solve the issue for the MX, it should be solved for the AP and switch too.
Do you have more information about the Telmex device? Since it's the first device in the path towards the cloud I suspect it's likely what is causing the issues.
Check if you can turn off the firewall on the Telmex router (unless of course you have other devices connected directly to it). All devices behind the MX will be protected by the firewall on the MX. More info here: