Relationship field of custom module "XYZ" not parsing in process email templates

Hi,

Relationship field of custom module "XYZ" not parsing in process email templates,variables not replaced in the email; eg: the variables still appear to the person who received the email:

At opportunity level we have relationship field of custom module "XYZ" and when we create opportunity we trigger email to users and our process email templates contains relationship field of custom module "XYZ" but its not replaicng with actual value.
And this was working previously, but stopped working all of sudden and we are unable to find the root cause for the same.
I am using variable in process email template of contacts module as below:
{::href_link::Contacts::XYZ_contacts_1::name::}

Can anyone suggest what might be the root cause for the same.

Thanks,
Shreya