It's due to the fact that when you added Responses Comments it added your Update item action into an Apply to each since there could be multiple responses. This will result in your List item being updated as many times as there are responses.
The actual error you are getting is because you are trying to access the Update item action outside the loop, so it doesn't have the right context.
What output did you actually want for the comments? What would it look like if you had multiple approver comments? Something like that below, or just all the comments without the approvers?
Example 1:
Approver 1: My comments
Approver 2: Looks great to me
Example 2:
My comments
Looks great to me
