Recently I've been getting this error a few times a day.
Slow down, you're making too many requests.
Please retry again in 4 seconds.
Error code: cloud_60_secs_limit.
I know I'm not doing too many requests, and this usually only happens at the busy times of the day.
I can see this website is simply hosted by Discourse themselves, but the only guess I can take at the cause of an issue like this is that this could happen when you're rate-limiting the CDN IP instead of the end-user IP. In that case you'd need to rate-limit based on the actual end-user IP which most CDNs report under HTTP headers like X-Real-Ip. But again, this might not be the actual issue, can't tell.