Mysteriosly Increasing Line Returns in Google Docs

I often create "To Do" lists in Google Docs. Normally, I hit the Return key twice after each item so that I have 1 line blank in between.

Occasionally I will go back to a document a few days later and suddenly there are 2 blank lines in between each item instead of the single one I entered. And if I go back a couple days after that, then there are 4 blank lines. And so on and so on! I then I have manually go through the entire list and remove all the extra carriage returns, which is extremely annoying and a waste of time.

This does not happen to all my Google documents, but it happens often enough that it's really frustrating me. I haven't been able to figure out any specific pattern as to which documents get affected. Has anyone else experienced this problem?

I should add that I occasionally view my docs on my Android phone via the GDocs app. However, I'm pretty sure this problem has occurred with docs that I have only viewed on my Chrome browser on my MacBook laptop.

Thanks in advance.