I had the same thing happen last week but
its was for about 10 days of dots with no events.
I turns out that I had a previous event set to last all day
but the end time of the event was accidentally set to
the day BEFORE the event. For some reason it added
the 10 dots/day with no events?
In the past AND identical start and end times/dates
The fixes above did not solve my problem because there is another twist. In addition to what others have mentioned about ending in the past, the dots fill every day if you schedule an event that begins and ends at the same time. For example, I had recurring birthdays set for 12am to 12am on the birthday (0 minutes). The extra dots disappeared once I changed to a 5 minute interval for these events (eg. 12am-12:05am). I changed Outlook, which is synced with the iPhone and cleared it up.