When configuring templates on an HTML field. If you use a line break, it will not be displayed. And will instead display as if no line break was configured within the template.
A template value configuration of:
Will be displayed as
within an HTML field.
This appears to be expected behaviour. You will notice that when using an HTML field in a template that 'Enter text in HTML format' message will display.
This is because HTML does not accept line breaks unless the command <br> is used.