A :suggestion with nothing in its brackets and no from has nothing to add and nothing to remove, so it renders nothing. Put the new text in its brackets, the text it replaces in from, or both.
Incorrect
To log in,
To log in, :suggestion[]{note="Too wordy."} enter your email.Correct
To log in, simplyToo wordy. enter your email.
To log in, :suggestion[]{from="simply" note="Too wordy."} enter your email.