why I am loosing the value of this array (@acc_list) after the first "while"?

Because that is the way you have programmed the loop:

while ( @acc_list ) {
 ...
 my @files1 = splice( @acc_list, 0, 100 );
 ...
}
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You've literally written, "remove (splice) the elements out of the array @acc_list in batches of 100 until the array is empty".

If you want to retain the values in the array, don't use splice.

You might use something like this instead:

for( my $p = 0; $p < @acc_list; $p += 100 ) {
    ...
    my @files1 = @acc_list[ $p .. $p+99 ];
    ...
}
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There are several other ways to code it, but that is probably the clearest.