Cards equipped with Samsung memory have no problems but models with Micron can suffer from flickering issues as well as poor memory overclocking. Micron-based cards can have issues with checkerboard patterns appearing, even when just mildly overclocked. Definitely strange that QA didn't catch this earlier.
The firmware update increases the GDDR5 memory voltage, which reportedly makes the problems go away. EVGA, Gainward and Palit have already issued updates, while ASUS, Inno3D, KFA2/Galaxy, MSI, PNY and Zotac still need to do so. Gigabyte reportedly did not use Micron memory.