Custom HTML field not showing in emails

Your software
My Mautic version is: 4.4.0
My PHP version is: 7.4
My Database type and version is: MariaDb 10.3

Your problem
My problem is: I have one instance that does not show custom html field in Advanced tab when I select code mode, the field is missing from the interface.

I have another instance of mautic that shows the field just fine:

These errors are showing in the log:
[no errors]

Steps I have tried to fix the problem:
I did a quick search it appears that the code for customHtml field is there, not sure where the issue is.

Has anyone experianced the same after the upgrade to 4.4? Any help is greatly appreciated.

Answering my own question here:

email template that had this custom html field was overwritten by my plugin. had to update the source and add my modifications at the end.