Well, just had a "spontaneous reboot" here. Using 5GHz., configuration is just fine, have latest firmware, always reset before and after upgrading firmware and manually re-entering settings. Drivers are definitely the latest, good cables, etc. *smile*. The wireless on my laptop disconnected, and when I looked at the front of the WRT1900AC, it was going through it's boot sequence. Didn't take very long, but I'm glad that I looked to verify that it was a reboot. I've had a couple of other disconnects, but have updated the driver on my wireless network adapter since then to the latest (as of 5/9/2014).
Anyways, guess I'll report it to Linksys, since this obviously should not be happening, and the more reports that they get, the more likely they are to fix it (I hope *smile*).
Edit: Any reference on how to report an issue or bug to Linksys...been looking around, don't see any obvious place to do that? Thanks!