This is probably too late for you, carl-w, I had a similar problem and found the following worked.
I was using the_field(‘fieldname’) which displayed the text content all on a single line.
Instead, use this…
echo wpautop( get_field(‘fieldname’) ) which then correctly used the line breaks in the original submitted text content.
Not sure if this issue is meant to be fixed with the latest update but I’m still experiencing the problem with version 5.2.0.
Thanks.
Same problem here with version (pro) 5.1.9.1.