There are specific controversies; take GNU vs OSI. GNU elaborates the differences on their site: https://www.gnu.org/philosophy/free-software-for-freedom.en..... I couldn't find OSI's take on their website, other than a general lack of reference to GNU/FSF's idea of Free Software.

Then there are disagreements on specific licenses. OSI approves licenses GNU does not classify as Free, and GNU classifies licenses as Free that OSI does not approve.

Then there's GitHub, which publishes a site to help you "choose an open source license," which includes a license not approved by OSI (the Unlicense), and only makes a reference to OSI as an "additional resource". Likewise, GitHub lists FSF as an "additional resource," while consistently using the term open source, not free, and not free and open.

Digital Ocean explains the difference between free and open-source software: https://www.digitalocean.com/community/tutorials/Free-vs-Ope....

Eliah Kagan answers the question on AskUbuntu with some explanation of the history and plenty of links: https://askubuntu.com/questions/78958/is-there-a-difference-....

In the past I've run into projects where the source was on GitHub where you could compile yourself, but binaries needed to be purchased. Lemme see if I can find it

There's plenty of non-free code on github, but it's still not open source and nobody seriously refers to it as such.

That is still free software and open source.

Epic's Unreal Engine is another example

Could you please elaborate?

It's shared source, behind a register wall. You can clone the git tree and privately hack to your heart's content, but commercial usage and sharing of the source are under (fairly reasonable) particular rules.