I’m having issues with WR21 and WR31 Digi Modems outfitted with ATT SIMs locking up. They are running FW: 220.127.116.11. Sometimes a 30-second power cycle fixes the issue. When the 30-second power cycle won’t fix the lockup, a reload or upgrade to the newer firmware will. I’ve noticed this issue happening a lot more frequently after the 3G to 4G shift with ATT. My WR21 and WR31 modems with Verizon SIMs installed don't have these issues.