CBP is not shut down, though they aren't being paid, so in principle they can still be processing GE applications. But if they depend on data (e.g. for the background check) from any agencies that are shut down, or contractors who are not funded due to the shutdown, then it's possible there will be delays. There can be a huge variation in processing times for no apparent reason, so it might just be normal-slow rather than shutdown-slow.

ETA: there's a thread over in the forum about it - GE centers are closed due to the shutdown.