Recently the publication of new posts containing custom fields has been behaving strangely. After saving the post, the system creates several other private null posts.
All this happens in a matter of milliseconds, I believe it began to occur after the new update.
There was an error that caused posts to be duplicated a couple of versions back, but I think that was cleared up.
I’m currently not seeing this issue on any or my sites or test sites.
The first step is to see if you can figure out if there’s a compatibility problem by deactivating other plugins and possible trying an unmodified 20XX theme.
It seems that the problem was caused by this plugin: https://br.wordpress.org/plugins/bnfw/ There is some incompatibility.
You might want to contact the author of that plugin. I looked at it quick, but can’t tell what the problem could be and I’m not familiar with it. They do support ACF, so they would have a better chance of figuring it out.