The advanced branch runs in parallel (instead of in-serial) leading to the unpredictable behaviour. Since each branch happens in parallel, the results will depend on when the branch is executed.

A particular use case in automation rules is:
1. We have a text field to take the list of users' account (either from API or from user input)
2. Create a smart value variable to hold all users' account
3. Use "Advanced branching" -> "For each: Smart value", edit another field (multiple User Picker type) with the smart value from step 2

In this scenario, the final users' account added into the multiple User Picker field is different with the text field. Each branch runs in parallel makes Jira to edit the field concurrently leading to the unpredictable behaviour.

We would like the advanced branch running in-serial.