This sounds like  issue 446246  actually. Next time it happens, could you see if scrolling with the arrow keys works? Or by dragging a scrollbar? Capturing and uploading a trace would be most helpful (see instructions in  issue 446246 )

Actually, this more appropriately belongs with issue 310649 since 446246 didn't mention history navigation at all.

Chrome 49 OSX.
- Scroll disappears without the need of navigating back.
- Scroll with arrow keys still works.

Trace attached. I just did this:

- Restart chrome (previous tabs were open).
- Use scroll in a tab (it is shown).
- Open a new tab to open chrome://tracing.
- Come back to the previous tab. Scroll no longer visible (but arrow keys do work).
- Then capture the trace.

After that, I come back to the previous tab and, somehow, scroll is visible. Then I select another tab, go back to the previous one and the scroll is again hidden.

I don't think there is a clear pattern, but I navigate without visible scroll 90% of the time.

Deleted: trace_no-scroll.json.gz 2.8 MB

trace_no-scroll.json.gz 2.8 MB Download

It is clear that I select some tab, I see the scroll bar during less than half a second, and then it disappears.

NOTE: Once the scroll has disappeared, if I move the pointer to the (now invisible) scroll bar and hold the mouse pointer there for a few seconds, then the scroll bar becomes visible again.