Timeline doesn't advance

Awhile back the timeline stopped advancing during recording and playing back in Ardour 4.6. I don’t know why this is happening. As you can imaging, it’s highly inconvenient. I’m sure there’s a setting for this, but I can’t find it. Can someone please help?

do you mean that it doesn’t follow the playhead? Ctrl-F on Linux/Windows and Cmd-F on OS X … toggles “Follow Playhead”