Not Python PHP, 85 83 bytes

while($argn[$x])$y=$s==strrev($s=substr_replace($argn,'',$x++,1))?$x:$y;echo$y?:-1; 

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Unnecessarily recursive:

PHP, 96 bytes

function f($a,$b='',$d=1){return$a?$c==strrev($c=$b.$e=substr($a,1))?$d:f($e,$b.$a[0],$d+1):-1;} 

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Not Python PHP, 85 83 81 bytes

while($argn[$x])$s!=strrev($s=substr_replace($argn,'',$x++,1))?:die("$x");echo-1; 

• -2 bytes thanks to @Night2!

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Unnecessarily recursive:

PHP, 96 bytes

function f($a,$b='',$d=1){return$a?$c==strrev($c=$b.$e=substr($a,1))?$d:f($e,$b.$a[0],$d+1):-1;} 

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Not Python PHP, 85 83 bytes

while($argn[$x])$y=$s==strrev($s=substr_replace($argn,'',$x++,1))?$x:$y;echo$y?:-1; 

Try it online!

Not Python PHP, 85 83 bytes

while($argn[$x])$y=$s==strrev($s=substr_replace($argn,'',$x++,1))?$x:$y;echo$y?:-1; 

Try it online!

Unnecessarily recursive:

PHP, 96 bytes

function f($a,$b='',$d=1){return$a?$c==strrev($c=$b.$e=substr($a,1))?$d:f($e,$b.$a[0],$d+1):-1;} 

Try it online!

Not Python PHP, 85 83 bytes

while($argn[$x])$y=$s==strrev($s=substr_replace($argn,'',$x++,1))?$x:$y;echo$y?:-1; 

Try it online!

Unnecessarily recursive:

PHP, 96 bytes

function f($a,$b='',$d=1){return$a?$c==strrev($c=$b.$e=substr($a,1))?$d:f($e,$b.$a[0],$d+1):-1;} 

Try it online!

Not Python PHP, 85 83 bytes

while($argn[$x])$y=$s==strrev($s=substr_replace($argn,'',$x++,1))?$x:$y;echo$y?:-1; 

Try it online!