Messages in Journal do not get timestamped correctly

I had to resize and move an ES disk, and though to myself that it'd be great to try out Graylogs journal this way. Theory being that I could kill ES, do my stuff, start ES and not lose a message.

The theory was fine, 14k messages were journalized until I brought my ES back. After a few minutes, the journal queue went to 0, but now the histogram looks like this (2 hours):


It would seem that the 14k messages that were processed, were either:
- Not processed at all
- Timestamped incorrectly (although I'm missing the 14k spike then)
- Not counted in the histogram

When searching the last 15 minutes, I get a 3.7k count (should include the 14k journaled) - so something is missing. It seems like the first option is the only one explaining this loss.