Hey @cacciaresi,
This issue is due to the fact that there is a load balancer (nginx) between the gunicorn process and the client. For some reason, the X-Forwarded-For header is not properly read by Django. That means that there is a problematic link somewhere in the chain:
nginx -> gunicorn -> django -> sentry
I think that the problem could be coming from gunicorn, which does not consider nginx as a trusted proxy. According to the docs, we should pass the --forwarded-allow-ips="*" option to the gunicorn process: https://docs.gunicorn.org/en/latest/deploy.html
Could you please open a github issue describing your problem and linking to this post?