contact variables from email templates no longer filled

we upgraded to version 7.9.1 and email templates which hold contact variables such as $contact_last_name are not being filled with the value when sending out an individual email.
I see those errors in the log files:

][ERROR] fromUser: Conversion of from user format Y-m-d h:i a failed
[ERROR] Unable to find relationship emails_email_templates
Wed Jul 19 16:39:35 2017 [20059][2018d567-f4b2-fe03-16a9-566ed9bc017b][WARN] emails_email_templates for emails_email_templates failed to load
Wed Jul 19 16:39:35 2017 [20059][2018d567-f4b2-fe03-16a9-566ed9bc017b][WARN] emails_email_templates for emails_email_templates failed to load

Wed Jul 19 16:39:35 2017 [20059][2018d567-f4b2-fe03-16a9-566ed9bc017b][WARN] Failed to load relationship emails_email_templates while saving Emails
Wed Jul 19 16:39:35 2017 [20059][2018d567-f4b2-fe03-16a9-566ed9bc017b][ERROR] Unable to find relationship emails_email_templates
Wed Jul 19 16:39:35 2017 [20059][2018d567-f4b2-fe03-16a9-566ed9bc017b][ERROR] Unable to find relationship emails_email_templates

and

[ERROR] Unable to load custom logic file: custom/include/social/hooks.php

It used to work fine but now it doesn’t anymore. Any help is much appreciated.

Hi, this is a known bug and has already been fixed in 7.9.3

however 7.9.3 had a new problem and you should just wait until tomorrow and install 7.9.4, that will fix your issue.