This came up twice very recently. The problem is that the use statements in the BEGIN block finish compiling before the BEGIN block does (seeing as the BEGIN block finishes later in the sources), so they get executed first.

In short, you want

use FindBin qw($RealBin);
use lib "$RealBin/lib/";
BEGIN { $ENV{APP_ROOT} = $RealBin; }
use MyApp::Conf qw/APP_NAME/;
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