I remember something about carbon formation at higher-than-expected levels at around 900 Myr, but I thought that particular paper was quite some time ago. Something along the lines of the hypotheses of carbon formation actually requiring on the order of 1 Gyr, which was even more problematic because the galaxy couldn't be even as much as 900 Myr.
Wish I could remember where I saw it...
On the mainstream front, folks are feeling joy at
finding primordial low metallicity clouds. Nathan Sanders there has some interesting comments on missing mechanisms for metal dispersion.