EKF2 Replay not reproducible

We are noticing a significant time delay when using EKF2 Replay. Below is an example, comparing z estimates. The blue graph is from the original .ulg file, and the red graph is from the replayed file (no parameter changes made). We are using v1.11

The replay consistently starts around 9 seconds in.
I noticed we get a message at the same time: [ecl/EKF] 34203730: EKF aligned, (baro hgt, IMU buf: 31, OBS buf: 23)