Tokens in form-triggered emails are not populating values when a new lead comes in through form fill out.
For the token to populate, the associated Marketo field shouldn't be empty and it must hold a value that will be passed to the token. It takes a small amount of time for the form to write the value to the lead record and it my not write all the info before the triggered email is sent. In case of new leads, using a wait step as the first flow step (before send email flow step) will be helpful. This will leave some time for the fields get their value filled from the form fillout. Once the fields have the value, the associated token will populate correctly during the email send.