Happened to me last night.  I had to reboot windows to fix it.  If it happens again, I'll try the suggested solution.
 
Paul

Yep the same just happened here, although it has done it intermittently in the past, now it seems like fixed behaviour - scroll bar is visible when playback is started but when the music goes beyond the edge of the clips view pane, the scroll bar disappears. I have disabled the "click" options as well, makes no difference.

joden
Yep the same just happened here, although it has done it intermittently in the past, now it seems like fixed behaviour - scroll bar is visible when playback is started but when the music goes beyond the edge of the clips view pane, the scroll bar disappears. I have disabled the "click" options as well, makes no difference.

Having the timeline stop scrolling is a different issue (and not a bug) from having the Now Time cursor disappear. Most likely you hit the Scroll Lock on your keyboard which stops scrolling independently of the Click Locks Scroll function.

The screen will also stop scrolling if editing while playing. To resume scrolling after editing, right-click on the time ruler.

Thanks Scook and Brundlefly - yeah guys I already knew all of that.. oh and BF the line is disappearing

Not solved. It's listed as a fix in X2a - "Now Time in X2 can disappear under certain conditions" but still randomly disappears on me and only closing and reopening the project will bring it back. Some seem to have success with toggling the inspector (I) to get it back.
 
 

Just to add to my post above - A PC re-boot does seem to fix it when it happens. And a re-boot is the ONLY action that does.

Still not solved. Sonar Studio X3c, Dell Inspiron 7737 with Intel HD graphics, win 8.1. Now Time cursor desappears from time to time, not very often though. I have to reopen the project in order to get it back.

This used to happen to me occasionally.  IIRC I could switch to a different screenset and back and that would fix it.

This happened so frequently with X2 that I decided to stop using it altogether. I hadn't been making much music anymore but decided to give it another go and so I bought X2 (shortly before X3 was released unfortunately) and an upgrade from Sonar 8.5 Producer. Obviously it takes some time to get used to the new version but I really got so annoyed by the Now time that went missing everytime, that at one moment I simply closed X2 and decided to spend my time more useful and forget about making music with it.
 
This week I thought about installing X2 again but I immediately thought about this bug so I considered upgrading to X3 (even though that would be a waste of money spend on X2). But now I read X3 also has this problem. I think that if I am going to make music again, I will install S 8.5 instead... I think this also has to do with me getting a bit older and sick and tired of learning new things everytime LOL