Scheduled reminders for activities not rendering custom field tokens

I have created some contact custom fields and scheduled reminders that include the custom field tokens.

So I have a reminder that goes out when an activity is scheduled. I include a custom field token in the mail message.

The token is not substituted in the message when the scheduled reminder is sent out.

If I send the message out as Actions>Send email to a specific contact, the token is substituted correctly.

Works OK in 4.6.10 but not 4.7 onwards.

Unfortunately I cannot replicate this on the demo site for you as outbound email is disabled.