Hello,
 
To summarize >>>
FXO --MP---SIP---MP---FXS
 
Fax transport was configured using G711 between the 2 MPs.
You have one FXO line dedicated to FAX on MP118 10.50.3.10 port 4
You fax device connected to MP118 10.50.3.12.
 
I updated the 2 ini configuration files for both MP118.
On 10.50.3.10 i created a new profile id 2 for the port 4 using t38 relay as fax method and I removed t38 from the default codergroup.
On 10.50.3.12 i updated the default fax method to t38 and also removed t38 from the default codergroup.
 
Configuring this way, the call gets connected using G711 coders. Once a fax CNG tone is detected a reINVITE will be sent to the other MP and the fax will be transmitted using t38 protocol which is far better than using G711.
Please load the ini files on the MP's and give it a try.
So please provide the new ini files and the syslog trace exhibiting the issue.
 
Note that :
1/ This kind of request is more implementation related than support related.
2/ I checked the support contract on both devices and it is expired since december 2016. So if further support is required you have to ask for support contract renewal.