The most likely explanation is the one stated in the error message. Your site is sending too many requests to the comments endpoint of Discourse.
- Are pages the Discourse comments appear on are being refreshed alot?
- Is your site experiencing heavier than normal load?
- Are the log messages continuing?
- Are you using the WP Discourse comment caching feature? If not, that would likely help here. You can enable comment caching in the settings.