Grok debugger works but logstash fails multiple lines

[Carlos_Fernando_Palm (Carlos Fernando Palma Roldan)]

Hello.
I am trying to use the following regex to capture some info from a log entry:

(?m)(?<=responses=)(.*)(?=extraData)

Now it works in the grok debugger:

But it fails in logstash:

Any idea why that might be the case?

Has it something to do with the use of the (?m) qualifier?