Been reading through multiple threads but didn't see one to address this.
I followed @RezaDorrani 's video here: https://www.youtube.com/watch?v=pA7pcAOvf10 to take the out of the box calendar screen template from PowerApps and customize it to use with a SharePoint list. It has worked for the the general structure of things. Where I'm running into issues is I think caused by my SharePoint list being an Events List. The need behind this is our users will be viewing the calendar from Outlook as well as within the app.
I nested a gallery inside the main calendar gallery to display the event names, but there doesn't seem to be any rhyme or reason to which item it displays in the nested gallery. I resized the child gallery to make sure they weren't just hiding. There is only one event showing up on any given day.
Here is a screenshot of what the Events list looks like on SPO:

This is what is showing up in my app:

In the OnVisible property of my screen, the following is set:
/*resets calendar view and date selection to today*/
Set(_dateSelected, Today());
Set(_firstDayOfMonth, DateAdd(Today(), 1 - Day(Today()), TimeUnit.Days));
Set(_firstDayInView, DateAdd(_firstDayOfMonth, -(Weekday(_firstDayOfMonth) - 2 + 1), TimeUnit.Days));
Set(_lastDayOfMonth, DateAdd(DateAdd(_firstDayOfMonth, 1, TimeUnit.Months), -1, TimeUnit.Days));
Set(_calendarVisible,true)
Here is my code for the items in my Child Gallery:
Filter(PILD_PTO,'Start Time'= DateAdd(_firstDayInView,ThisItem.Value, TimeUnit.Days))
This is how the galleries are set up in the app:

I tried watching videos from @Shanescows to get tips too but couldn't find a solution.