Reproduces on 66.0.3326.0

Reproduces in 65.0.3325.0

Appears not to reproduce on 64.0.3240.0 (for such a bad bug, this is a long time that it has been allowed to sit).

Still can't reproduce with the official 64.0.3240.0 build, but I can reproduce in every step of a bisect, through to r508910, which gives a bisect range that is not useful.

Maybe my machine is messed up?

Likely related to scroll latching changes we made in M65 which unmasked a number of bugs in our pipeline.

How frequently can you repro? We've been chasing similar bugs in issue 797708 for a while now - fixed a bunch but still hear occasional reports. That one is now specifically tracking a bug in scroll animation code but I think Mac doesn't use smooth scrolling (due to wheel being rare?)

There was another bug where alternating wheel and touchpad would cause them to stop working. That should be fixed in stable though too.

We've added logging in traces so if this repros reliably it'd be helpful to capture a trace where the scroll stops working in Canary.

 ccameron@ thanks for the report and bisect. Could you please confirm if you use a combination of external mouse and touchpad?

>There was another bug where alternating wheel and touchpad would cause them to stop working. That should be fixed in stable though too.

Both the bug and the fix here was ChromeOS only, but there might be a similar issue with alternating between the two scroll devices on Mac.

Can you fix it by scrolling with other methods and retrying wheel scroll again?

> How frequently can you repro?

I got pretty good at this -- ~90% of the time I was able to repro it.

> Could you please confirm if you use a combination of external mouse and touchpad?

This is using the scroll wheel of an external mouse. I haven't had this happen with a trackpad.

> Can you fix it by scrolling with other methods and retrying wheel scroll again?

Yes, if I scroll by, e.g, click+drag (or IIRC arrow keys), it will go away.

Let me know if there's any instrumentation I can add/dump to help debug this!

What screen are you using? Does it also happen on a mac laptop (with external mouse)?
What happens if you change the body overflow to auto or scroll?

Does waiting for a second, or moving the mouse fix the issue?

If you could capture a chrome://trace where it goes from scrolling->not_scrolling that would help us narrow down where the issue is.

Re #9:

> What screen are you using? Does it also happen on a mac laptop (with external mouse)?

This is with 2 non-retina screens attached to a retina laptop using an external mouse.

> What happens if you change the body overflow to auto or scroll?

(sorry, not sure)

> Does waiting for a second, or moving the mouse fix the issue?

Moving the mouse sometimes fixes it.

> If you could capture a chrome://trace where it goes from scrolling->not_scrolling that would help us narrow down where the issue is.

Sure, what categories would you like?

> Sure, what categories would you like?

blink, browser, cc, input, compositor, content, event, input, latency, latencyinfo, renderer, renderer_host, renderer.scheduler, ui, WebCore

friendly ping for a trace on canary or dev. (version 67 does not have some of the new tracing logic added for scrolling.)