Regular readers will recall that yesterday AT&T suspended the rollout of the Android 4.3 update to its carrier-branded version of the Galaxy S4. It looks like US Cellular is doing the same today. The following is a statement given to Android Police when we asked a US Cellular representative about any possible delays to the update, which was started on November 8th:
We have suspended the release of the Android 4.3 upgrade for the Samsung Galaxy S 4 at the request of Samsung. This was a global decision made by Samsung and we are working with them on a new resubmission of the software and will have more details soon.
So, mirroring AT&T's statement on the suspended update, there are no concrete reasons as to why the update was pulled or when it might be coming back. You'll note in that carefully-crafted wording that there's no indication of a bug or other problems; an AT&T representative mentioned that either they or Samsung were "investigating some issues."
The delay is particularly annoying for GS4 users because in addition to an upgraded version of Android, the latest Jelly Bean update was set to add compatibility with the Galaxy Gear smartwatch, among other enhancements. So far AT&T and US Cellular are the only carriers to suspend the active update, so either other carriers aren't so quick on the trigger, or they'll be implementing whatever changes there are in a later patch.