@Pietro Turrin, you need to use the Max Wait Timer so the token will advance/loop back to the top of the block of activities and try to pull an Operator and continue the work. If you didn't use it, the token would stay on the Push to List activity indefinitely and the work would stop.
The reason there is an error is because the Push Value in the Push Operator activity needs to be token.Operator, not just token. Also, the OperatorGrey Operators need to have the lastDrinkTotalTravel label added to them (and the Automatically Reset option used) in order for the logic in Water Breaks to work.
I also realized when the Pull from List activity in Water Breaks does pull an Operator, there is nothing in the Operator Tasks logic to prevent that Operator from being pulled again. So I adjusted the model a little to fix this, along with the other fixes, and I am including the modified model here (tu0-comb-v4-break_FS1.fsm).
The biggest change was to have an initial Pull Operator activity that pulls the Operators when the model first starts. Then, in the big block of activities in Operator Tasks, there is another Pull Operator activity that only pulls a specific Operator (as part of the Query/Object/Array field). This way, when an Operator is pulled out because of the Water Breaks logic, it won't be accessible in the Operator Tasks logic until it finishes the water break.