By the way if I keep an eye with "du -h" on the elasticsearch folder it goes from 5.1GB down to 4.1GB then up again and then down... WTF is this normal? Should I be worried?
Rebuilding caches usually shows the id of the record in the database and not the number, so if you did e.g. a test import of 1000 posts, then delete them, your id will go from 1000 to 2000.