I have the same or similar problem, and it just started. When I return to a Note, many of my paragraphs, which I separate with double spaces into block paragraphs, will have merged into one long paragraph. Others remain normally formatted. I don't use tables or photos or anything else to cause this behavior. I just write.
P.S. For instance, if this were a Note and I closed it after syncing, when I open it again the "Liam" would appear directly under the paragraph without the double space, while the P.S. might retain its spacing.