Multiple singe day events grouped as single consecutive day events

Classic gap and island analysis. Here is an article introducing the topic and how to accomplish what you are trying to do: https://www.red-gate.com/simple-talk/databases/sql-server/t-sql-programming-sql-server/introduction-to-gaps-and-islands-analysis/

An alternative way in MagicETL would be to use a lag function and have some logic that if the previous value is not the current value minus one then that current value must be a new start to an island (the 5th in your example). Similarly you could do a lead function and anytime the future value isn't the current value plus one then it is the start of an island (the 6th in your example).

I think the linked article is the cleanest way to do this in a MySQL dataflow.