Not able to assign value to Tracking variables in Loop

Summary

Not able to assign value to Tracking variables in Loop

Content

Hello,

I want to assign value to Tracking variable $tracking_var_2 and 3 inside for loop. I want to use this variable value in global fault to send notification. I can see tracking variable in mapping inside that loop but not in Assign variable activity. 

Does anybody have faced similar issue? appreciate if you can help me to resolve this issue.

Attaching screen shot for the reference.

 

Thanks,

Hemen