Thank you for posting this solution! This resolved my issue as well.
One of our applications writes logs multiline where all starting log entries start with the date itself. For example:
2017-02-09 04:00:21.517 C010 .... blah blah blah
2017-02-09 07:38:44.507 A5B4 .... we love all datas.... blah blah
The pattern you provided here works PERFECTLY. Thank you again @mmuszkow!