I tested blocking a date on my calendar using my iPhone and adding a note and had no trouble. A black dot appears on the date that is blocked and if you click on that date, I can see the mention along the lines of " 1 remark" (my listing is in French so am translating what you might see in English). If I click on that I can see what I wrote. I presume that when you wrote your comments in notes, you clicked the SAVE button?