My guess is the HTML you're suppling has non-HTML linebreaks. We convert non-HTML linebreaks to HTML linebreaks during HTML emails now to fix issues with linebreaks not working as one would expect. Adjust the contents of your email to either not have non-HTML linebreaks or convert them to HTML linebreaks yourself where intended and remove the rest.

It can't be turned off. Removing it would require modifying core code, which you will lose those changes every time you update CB. Below is where this is done.

IN: libraries/CBLib/CB/Legacy/LegacyComprofilerFunctions.php
ON: Line 349

I understand this is frustrating for you, but to understand why it was done is because 99% of our email configurations are just textarea fields and people tend to not add br tags for a linebreak and instead just do a text linebreak so we convert these for them. This helps the vast majority of our users, but does cause problems in cases like yours.

Will review adding an option to skip this when using mass mailer as that's our only WYSYWIG email or to skip it globally.

forge.joomlapolis.com/issues/9128

As explained above most of our email parameters are textarea fields. They are not WYSIWYG fields. Users expect their linebreaks in the textarea fields to persists. They will not unless we convert them for them. We've only I believe 2 WYSIWYG emails (mass mailer and cbsubs mailer). A feature to toggle this off at the API level is being reviewed for a future release so those emails will skip doing this behavior.