I have posted a video that demonstrates the reboot issue I've been seeing:
https://www.youtube.com/watch?v=tf0YHXq4fk8
And captured a couple of other issues as well:
- Internet intermittently being dropped, but not sure if this is a problem on the WRT1900AC or the UVerse Gateway router.
- Upon rebooting after it crashes, about 10%-20% of the time I have one switch port that won't reconnect. That particular port is connected to a Linksys SD2008 gigabit switch and it doesn't always want to re-establish a connection. Cycling the power on the SD2008 switch seems to get the link going again. I'm not sure if that's a problem with the WRT1900AC, the SD2008 switch, or maybe the cable. I had no issues with it in the same configuration with my previous router (Netgear WNDR3300).
Scrolling down into the video description on YouTube, there are clickable timestamps that will take you to the main points of interest. It's a long and boring video...it took over 20 minutes to get it to reboot and the port that didn't reconnect added a few more minutes to the video.