Looks like another instance where the object and tied hash get DESTROYed in an odd order. Note that the DESTROY() for DBIx::Threaded::db wraps the same code in an eval{} to make it go away, so I'd suggest trying the same. Just edit your copy of Threaded.pm at line 1727 to

    eval {
    $obj->{_inner}--;
    $obj->_send_simplex('DESTROY')
        unless $obj->{_inner};
    };
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and that should silence the errors.