ryo

/wp-includes/class-wp-image-editor-imagick.php のバグが原因

370行目以降の

  /* If alpha channel is not defined, set it opaque.
  *
  * Note that Imagick::getImageAlphaChannel() is only available if Imagick
  * has been compiled against ImageMagick version 6.4.0 or newer.
  */
  if ( is_callable( array( $this->image, 'getImageAlphaChannel' ) )
    && is_callable( array( $this->image, 'setImageAlphaChannel' ) )
    && defined( Imagick::ALPHACHANNEL_UNDEFINED )
    && defined( Imagick::ALPHACHANNEL_OPAQUE )
  ) {
    if ( $this->image->getImageAlphaChannel() === Imagick::ALPHACHANNEL_UNDEFINED ) {
      $this->image->setImageAlphaChannel( Imagick::ALPHACHANNEL_OPAQUE );
    }
  }

クォートで囲って！

  /* If alpha channel is not defined, set it opaque.
  *
  * Note that Imagick::getImageAlphaChannel() is only available if Imagick
  * has been compiled against ImageMagick version 6.4.0 or newer.
  */
  if ( is_callable( array( $this->image, 'getImageAlphaChannel' ) )
    && is_callable( array( $this->image, 'setImageAlphaChannel' ) )
    && defined( 'Imagick::ALPHACHANNEL_UNDEFINED' )
    && defined( 'Imagick::ALPHACHANNEL_OPAQUE' )
  ) {
    if ( $this->image->getImageAlphaChannel() === Imagick::ALPHACHANNEL_UNDEFINED ) {
      $this->image->setImageAlphaChannel( Imagick::ALPHACHANNEL_OPAQUE );
    }
  }

無事画像がアップデートできるようになりました。
リリース前にちゃんと動作確認してるのか？＞wordpress