This drove me nuts for quite a while too.
On PC, there is a keybind for "autorun", which is by default bound to 'G'.
Try pressing G during combat and see if it works. If it doesn't, check your keybindings to see if this is bound to something else.
It was during the menu as well. Not just during gameplay. The keybindings were the first thing I checked. haha.
I talked to EA Help and they suggested I do a UO trace which was pretty bad. They thought maybe it was a bad download? Anyway, I downloaded directly (instead of through my router) and it seems to have worked? I'm going to play a bit more before I definitely call it a solution though.
