Formula switching from IF TRUE to IF FALSE

Hi there!

I am trying to find the average distance of the distances in column A if that trip falls between dates of Period 1. (Please see attached file).
This is my formula: =AVERAGE(IF(($A:$A>=G18)*($A:$A<=H18), $C:$C)) and it works!

The issue is when I copy this formula to follow dates of Period 2, then Period 3 etc it provides a 0 as the answer which is incorrect.
This is my formula: =AVERAGE(IF(($A:$A>=G19)*($A:$A<=H19), $C:$C))

As you can see the only thing that has changed is cells in column G and H which denotes the dates that I need to average calculation to fall between.

Please help!