Quirky but sometimes when I have this issue where I add a line break I will hit the space-bar a couple of times in the empty line and it seems to do the trick.
Well that was simple but it worked!
What email client are you using?
What email template are you using?
Is the whole text + CTA a unique editable zone ?
The simplest way to add some spacing above a below a CTA which is usually made of a table is to add some empty rows to that table. Empty meaning with a character in them.