Hello,
I guess, there is something to do in your Item custom field configuration, and more especially in DISPLAY : MAIL part.
See this screenshot :
Check that you have the Email display switch is
On, and better I think you can have a look on your Item custom field Configuration of your visible custom field on your screenshot to reproduce the same configuration in the
DISPLAY : MAIL part.
Other point to check, check if you have
override on your emails that may leads to this results, try to disable it.
Regards