They have taken over the ACF plugin in the plugin store. In an intransparent manner. It is GPL licensed, but had a pro license and features sold. And still does have them on their publishers side.
A strength of the GPL is that the community can fork and take over projects.
At the same time, and this instance is such a case, on a centralized platform, projects can be taken over instead of be forked.
They developed and published a plugin. Now it's been taken over by someone else, on the primary distribution and discovery platform, and they have no control over it. Worse than that, the takeover now offers their sold functionalities for free now.
This makes the "open source but not free, but after two years true FOSS licensed" licenses look very useful if not necessary for businesses and developers that want to monetize. At the very least when they [have to] use centralized platforms.
OS stands for "Oh Shit!"