When I call it with Exporter like this:

package Methods {
    use strict;
    use warnings;
    use feature qw(isa);
    use Logic::Easy;
    use Exporter qw(import)
    no warnings qw(redefine);
    our @EXPORT_OK = qw(frobnicate);

    sub frobnicate : Multi(frobnicate) {
        SIG [$o] where {$o isa 'Foo'};
    qq(foo);
    }

    sub frobnicate : Multi(frobnicate) {
        SIG [$o] where {$o isa 'Bar'};
    qq(bar);
    }
    1;
}

__END__
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#!/usr/bin/env perl

use strict;
use warnings;
use lib q(.);
use Bar;
use Foo;
use Methods qw(frobnicate);
use feature qw(say);

my $gizmo = Foo->new();
my $mojo  = Bar->new();

# dd $gizmo, $mojo;

say frobnicate($_) for
    ($gizmo, $mojo);

__END__
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I get:

karl@h3002993:~/src/perl/mmdemo$ ./run.pl
Logic::Easy control failed at Methods.pm line 16.
 at Methods.pm line 16. </p>
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The same result with say frobnicate($gizmo);. With say frobnicate($mojo); i get bar.

With the loop and Methods::frobnicate($_) i get the expected result.