The issue that Microsoft has been dealing with is a GSOD error caused by a "common scenario" around gaming anti-cheat codes. Windows Insider head Dona Sarkar explained on Twitter the other day that the fix was ultimately out of Microsoft's hands, and that the company was essentially left twiddling its thumbs (or more accurately, Slow ring subscribers were) while its third-party partner worked to resolve the issue.
"Looking at our Slow ring population, MANY of you play these games so your machines would be very difficult to use—we are committed to releasing Slow builds that are high quality so this is why we're holding the build," Sarkar said.
Sarkar never mentioned which specific games were affected, but Microsoft is forging ahead anyway in the Slow ring. However, even though there is finally a new build available to Slow ring subscribers, PCs with the base language ZH-CN will not receive the update. Furthermore, Microsoft has taken matters into its own hands and put an update block in place for users of the most common games that are impacted by the GSOD error.
"If you uninstall the affected games, you can get the update," Microsoft says.
In short, Microsoft is pushing out a new build to the Slow ring, but is also blocking it to anyone that has the anti-cheat software installed. It's a serviceable workaround, though Microsoft still has not said exactly what games are causing the headache.
On a side note, the reason users are seeing a GSOD instead of a more traditional BSOD (blue screen of death) is because Microsoft has gone green on its Insider builds. It's the same thing, except the different colors make it easier to distinguish between Insider and production releases.