please get someone to fix the "Paragraph" section of this page to teach your users the two-space requirement: https://confluence.atlassian.com/bitbucketserver/markdown-syntax-guide-776639995.html
The above part is a bug (either in the documentation or in the implemenation, you choose - see Issue
#7396 for reference), the below part is more of an enhancement request:
PS - it's also worth noting that bitbucket is kind enough to import a texty version of the changelogs into a Pull Request, which includes 4 spaces at the beginning of lines that fall under each commit. If there was any way bitbucket could automatically interpret these 4 spaces (which are always after a CR) as an instruction to display a CR on the pull request page, instead of removing the CR that is mid-paragraph, that would make it look awesome and be fully automatic.