Unfortunately, I couldn't reduce the testcase, so please take the following steps to repro:

1. On ToT open DevTools for a page.
2. Go to Performance panel
3. Right click and load the attached timeline
4. Drag the timeline so the time mark of 323ms be in the center of the screen.
5. Notice a small blue ticks drawn around this time position (see the SS)
6. Zoom in with mouse wheel while keeping point 323ms on the screen.
7. Notice the blue lines disappear at certain zoom, and then appear back as you continue to zoom in.

The blue lines should be visible on all zoom levels.
 

Deleted: Profile-20170328T150224.json 5.6 MB

Profile-20170328T150224.json 5.6 MB View Download

Deleted: Screenshot from 2017-03-28 16:01:23.png 62.2 KB

	Screenshot from 2017-03-28 16:01:23.png 62.2 KB View Download