With pipeline.workers set to 1 and pipeline.ordered set to true, logstash should process the events on the order they happen, but I'm not sure that this will guarantee that the events will be processed in the same order in Elasticsearch side.
Searching the forum I found this post on a topic that says that the user should not expect that the operations on a bulk request will be performed in order, not sure if this is still true, maybe someone from Elastic can provide more feedback.