Calendar not showing all items in month view (not overflow, just not showing)

A have items, all the items contains a column named “Fecha eHES Aprobado”, that columns is a date when an event ocurrs. Using a Status column i can say if the event was on time or not.

Now with that information i would like to put everything in a calendar widget to see in my month, what activities where on time or not. But the month view doesn´t show all the data. Keep an eye on september 16.

i´m not using any type of filtering, in fact if i go to the week view i can see the missing data.

I try to fix that enabling/disabling the hide weekends view, creating the calendar in a new view, changing the view size, making sure that the “color by” or “the date columns” were right and they are right.

For me this is clearly a bug.