I kept losing connection throughout the lesson and because of that I lost more than 5 minutes of lesson time.
「レッスン中に何度も通信が切れて、合計で5分以上レッスンが短くなった」 は英語で I kept losing connection throughout the lesson and because of that I lost more than 5 minutes of lesson timeになると思います。
I kept losing (internet) connectivity throughout the lesson... もしくは The internet connection kept randomly disconnecting throughout the lesson ... もいいと思います
Disconnect - 接続が切れる、切断する
インターネット回線が不安定 - Unstable internet connection (接続が不安定)
イギリス 
