During the 4G outage today, I noticed that the status indicated I was connected to EVDO RevA:8 instead of eHRPD:13 like usual. I keep mine forced in 3G all of the time for the battery life (2+ days of standby with Auto-sync turned off and minimal use) and only switch to 4G occasionally.
Anyway, as I understand it, you only see EVDO show up under status if they have forced you over manually during an outage, and I also noticed the issue with tethering which caused me to instantly suspect it as the culprit. Low and behold, when I switched to 4G, it connected just fine; then, switched back and verified that it was still occurring, and most interestingly noticed that 3G was still grabbing EVDO rather than eHRPD. Toggled it again - same deal; then Airplane-mode - ditto. Had to power-cycle before it grabbed eHRPD again and now tethering is back up and fine in both 3G/4G.
Hope this helps. Maybe the Devs can take a look and see if something can be done, but this will mean that during outages when we're forced to 3G-EVDO, tethering will NOT work...