Fix a problem on contact odoo 12 running on AWS EC2 -Looking for Odoo Long term relationship-

We have an odoo12 (community edition) running on AWS EC2.
This application is multi-site (routed through AWS) and multi company.
We have no custom module except a dedicated form https://opex.academy/LeadContact to collect leads
This form creates 3 custom fields to identify a contact (company category, status, role)
Recently we have a problem is creating new individual employee through a company getting this error:
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Error: Odoo Server Error
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/odoo/tools/safe_eval.py", line 352, in safe_eval
return unsafe_eval(c, globals_dict, locals_dict)
File "", line 14, in <module>
AttributeError: 'res.partner' object has no attribute 'child_id'
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Before starting we need a complete backup of the image.