You have the following piece of code, where I guess you want $Lastrow3 to be interpolated but, since it is inside a single-quote, it doesn't.

$Sheet->Range("H$lastrow4")->{Formula} = '=sum("H17:H.$Lastrow3")';
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Try changing it to the following

$Sheet->Range("H$lastrow4")->{Formula} = '=sum("H17:H.'.$Lastrow3.'")'
+;
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