@ACES
I have tested this with v1.14.2 and PHP 7.4 and I cannot replicate your issue.
I added a Custom Field on the Contact Information Form and set the var to custom_user_field
:
I then went to a User's Account and filled in a value for this field:
I added the var to the Template:
I responded to the Ticket and the User received the correct value in the Alert:
Cheers.