It's disappeared for me a few times, generally a reboot and then toggling it on and off fixes it. That said, I hate the bar. There is no good placement for it where it's both easy to reach and doesn't get in the way. I setup tasker to manually launch it with Shortcut > Side Sense Window Manager.
Shoot now mine disappeared and won't come back. I had it disabled but now I miss the little guy...
Edit: Trying to see if I can restart the service manually but not sure which one and I can't quite get the format right to launch any of them yet.