PC/NA, DC Templar (cp1740 or so). While exploring Blackreach, my character keeps going briefly into combat status, then out of combat again, without any NPCs or enemy mobs nearby. This happens both randomly (about every 30 seconds, but not on a timer) and also whenever I loot a resource node. No idea what is causing it. Have not tried disabling addons yet, but will do that to see if it makes a difference. (I later tried disabling addons, but the "in combat" status is not as easy to see when you don't have an addon that says you are going into combat.
It still happens though).

Update June 8: still happening. Last night this issue was most apparent in the Dusktown Cavern, but also in other parts of Blackreach. The "go into combat when you loot a node" part seems to have gone away though. Sometimes there is a cluster of several "combat" events in short order, then nothing. Others in zone said it happened most often near a wayshrine for them; it may be related to number of other players nearby - or possibly to enemy mobs that are VERTICALLY nearby (below ground)? For me, it's most visible when I'm moving, but not specific to a location - go back a pace or two and the effect does not repeat.
One visible effect is that when you are doing the main quest with Lyris as a companion, she will unsheathe her axe and then put it away. Others mentioned using a special crafting location and having a red border on their UI every now and then. Further testing required.