There hasn't been a new Slow Ring version of the Windows 10 Insider builds for some time now. Microsoft Windows Insiders chief Dona Sarkar explained on Twitter that this is due to a bug caused by gaming anti-cheat software.
Sarkar notes the issue is out of Microsoft's hands as it's caused by 3rd party software. Microsoft is working with them on solving the problem, until then there will be no new Slow Ring release because many users play these games.
(1/2)Many of you are asking why we haven't released a #SlowRing flight in a while. We have a GSOD that's caused by a very common scenario around gaming anti-cheat codes. Unfortunately the fix is in the hands of our 3rd party partner company that we're working with them on...
(2/2) Looking at our #SlowRing 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