Gunicorn preload flag not working with latest XGBoost version (post 1.6.0)

We have an XGBoost model served via a Flask app on Heroku. This Flask app is launched using gunicorn.
We are using the `--preload` option of gunicorn in order to mutualize memory consumption of the several workers that are launched (4).

This setup was working well until the upgrade to version 1.6.0 when it stopped working. Now the predict function of our XGBClassifier hangs forever.

**Environment:**
```
Flask==2.1.2
gunicorn==20.1.0
numpy==1.22.4
xgboost==1.6.1
```

**Gunicorn command:**
`web: gunicorn --preload -w 4 run:app`

**Error:**
```
[2022-06-29 18:18:31 +0200] [17983] [CRITICAL] WORKER TIMEOUT (pid:17984)
[2022-06-29 18:18:32 +0200] [17983] [WARNING] Worker with pid 17984 was terminated due to signal 9
```