Welcome to RHL EPOCH 2.0! Counting Difficult Win Streaks since 25-08-2017 after the new Match-Making update came out.
Score Based Mode is very similar to DBWS ranking with the only difference that each war win here will earn your clan an individual Score per Win value based on the Difficulty and Engineering in the recent wars (check your current Score per Win on your clan's page). Scores are being added up while you keep winning, but when you lose it is reset to zero - just like usual win streak. This system allows clans with higher difficulty to take high places without getting the longest win streak.
A current clan's score described above is called Win Streak Score (WSS) here. And the best such score ever achieved is Best Win Streak Score (BWSS) respectively.