From the developer website (notesplusapp.com)
IMPORTANT: We’ve found out a serious bug in v3.0 that makes text vanish after a page refresh if it contains the “&“ and “<” characters. This has been fixed in v3.0.1. For now, please avoid these deadly characters in your notes. We sincerely apologize.
So I think then that it is that what you are experiencing? Maybe for now type 'and' instead of '&' etc..