1) We are sincerely so sorry for such inconvenience we happened to cause to you. 「happened to cause to you」がミソ。「今回たまたま不便をお掛けした」の意で、 問題発生の常習性を否定した言い方です。
対象問題点に付いては、 Please allow us to have enough time to confirm the alleged problem before we report to you on this matter. と伝え状況把握を開始しましょう!