@RezaDorrani created a fabulous walkthrough on how to set up a calendar in Powe Apps. (https://www.youtube.com/watch?v=pA7pcAOvf10&lc=UgwZxNRn0pQmStbIvE94AaABAg.9n_qLZ-VNYe9nriqdWcVr9)
I have implemented this with great succes but have hit an issue I can't resolve. Am posting this here to provide more detail and see if anyone can help.
The calendar gallery is a 7x6 grid - making it 42 boxes showing on screen. The Items property is as per Reza's video, and is unchanged from the out of the box solution that was copied:
[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41]
The screen is showing as - (Today - 30) March:

This screenshot above shows the last 3 rows of 7 blocks. The blocks at the bottom are actually for 2,3,4,5,6 and 7 April but don't show the day number Text labels. (the colored items are for 3,4, and 5th of April)
When I move to April, the bottom three rows shows like this, with day number labels showing:

May, June, Aug, Sept, Oct, Nov last three rows looks like this:

July, December:

So, whenever the last row, first column is a day in the current month, all good, the day number labels show. If it is in the next month, no labels.
The formula for the Text property of that Text label is:
If(DateAdd(_firstDayInView,ThisItem.Value,TimeUnit.Days) = Today(), "Today - " & Day(DateAdd(_firstDayInView, ThisItem.Value, TimeUnit.Days)), Day(DateAdd(_firstDayInView, ThisItem.Value, TimeUnit.Days)))
The fill property for that Text label is:
If(Weekday(DateAdd(_firstDayInView,ThisItem.Value,TimeUnit.Days))=1||Weekday(DateAdd(_firstDayInView,ThisItem.Value,TimeUnit.Days))=7,Color.LightGray,
If(DateAdd(_firstDayInView,ThisItem.Value,TimeUnit.Days)=Today(),Color.LightBlue,
ColorFade(RGBA(56,96,178,1),80%)
))
I am lost as to how to fix this. Any help greatly appreciated.