Hello @Marius_Dragomir
All the data isn't from 2018. Changing the search time to 5 years didn't work.
The issue started on 11th December when I upgraded Elasticsearch and Kibana to 7.4.0 from 6.8.3. Index temp-http has been present since the beginning with the timestamp field format as "EEE, dd MMM YYYY HH:mm:ss z". But after the upgrade, it doesn't seem to work in Kibana discover.
On the other hand, I created index http-logs after the upgrade with timestamp field format as "MMM dd, yyyy HH:mm:ss.SSS" and it works. Not sure what got messed up.