Discrepancy in weather files

I was testing some radiation studies and found this discrepancy between different weather files.
It only occurs for some very specific dates - 22 Dec being one of them
Please refer to the image of sky domes below -

The EPW files used in the study are TMY and RMY from Sydney Airport.

Is this a common issue between different weather files?
If yes, is there any way of knowing or testing what these problematic dates/timeframes might be for different weather files at same location?