I have APO set up (correctly according to documentation).
Auto-purge in the Wordpress plugin states “This feature is superseded by Automatic Platform Optimization for WordPress. If you are using APO, then this setting should be disabled.”
I noticed (non logged-in) user comments were not posting and heard from some visitors they were having issues posting comments. I was able to replicate in private windows.
Contrary to the above documentation, I turned on auto-purge and my test comment was able to make it through (which is good, but contrary to the documentation).
Update: It seems that some users are still having issues getting comments through, so at best, APO is intermittently permitting comments/purging. All spam filters and caching plugins (other than Cloudflare) are off. Does the WP plugin w/ APO work without issue with Wordpress commenting or not? It does not seem like it. If so, the documentation on proper implementation seems incomplete.