Do you use a custom template or variation or position?
No
How do you call your field?
Not sure what you mean here.
It is a plain text input field which loads in the user profile.
If you mean how I name the field, it is called field_length (as in football field)
In any event, this is the field that stores the values, not the dynamic select list which retrieves the values.
There is field_length to store values and field_length_picker to query them from search form.
What's the storage config of the field?
Custom > Free > field_length (a dedicated column has been added to cck_store_item_users)
Do you use multi values option?
No.
Is there only this field concerning by the issue?
Nope. There are two. Please see above.
No issue to render Joomla plugin field?
Not that I have noticed.