Some users are reporting sporadic issues.
One of the main selling points of the new MacBook Pro—other than the ridiculously fast processors—is the abundance of ports, including the return of the on-board SD card reader. But according to early users, it’s not working as well as it should.
As reported by Macrumors, several MacBook Pro users are reporting “super flakey and inconsistent” performance with the SD card reader. The reports are somewhat varied, but seem to be related to the reader rather than a specific card, with the issue affecting various types and models.
The new MacBook Pro supports several varieties of SD card, including MultiMediaCard, Default Speed, High Speed, UHS-I, and UHS‑II cards. MiniSD and MicroSD are also supported via an adapter. The issues described appear to be software related and not due to failing hardware or incompatible cards.
Read more at MacWorld.com