This is another repro (maybe 25% success):

- Have 3 tabs (code review page https://chromium-review.googlesource.com/q/goodix+status:closed , wikipedia https://en.wikipedia.org/wiki/Cat , and new tab page)
- scroll w/ two fingers on Wikipedia
- ctrl-tab onto NTP
- use mouse to click onto code review page
- click on code review page somewhere that does nothing
- use mouse to click on wikipedia page
- try to mousewheel scroll

At this point you either hit the repro or try again

Based on the repro steps looks like the bug will happen rarely:
You need to switch the tap while you are scrolling with trackpad, and then go back to the old tap and use mouse wheel and the repo is successful 1-2 out of 10 retries.

If the problem is not reproducible with simpler steps and/or more reliably, I don't think it's a p1 bug, adlr@ could you please confirm?

The repro steps certainly don't look like something that would happen often, but I am hitting this issue without trying to as soon as I connect my Pixelbook to the docking station (with external mouse).

BTW, I now have an even easier repro case:

- scroll with two fingers on touchpad
- stop scrolling, but keep fingers stationary on touchpad
- ctrl-shift-tab to switch off the tab
- use mouse to click back onto tab
- try to scroll with the mouse

I suspect where this is really impactful is when users switch off tabs when in laptop mode. Later on, they connect a mouse and many of their tabs are already in this bad state.

please re-categorize if my pick during triage was wrong

Re comment #4:  As soon as the user starts scrolling with touchpad while their fingers are still on the touchpad the mouse wheel scrolling wouldn't work, lifting the fingers from touchpad restores mouse wheel scrolling.

adlr@ in your repo steps in comment #4, do you lift your fingers from the touchpad? and if you do in what step you do that? When you lift your fingers are you able to restore scrolling with mouse wheel?

I added finger lifting to the sequence below:

- scroll with two fingers on touchpad
- stop scrolling, but keep fingers stationary on touchpad
- ctrl-shift-tab to switch off the tab
<< lift fingers here
- use mouse to click back onto tab
- try to scroll with the mouse

Lifting fingers doesn't help restore mouse wheel, which I think is what this bug is all about.

seobrien@ (who is on paternity now) mentioned there is a scrolling in progress flag that may be stuck on in this case, which sounds like what you're saying as well.

Thanks so much for your help on this!

The root cause for this bug looks like the same as  crbug.com/838457 , I'll keep them separate for now to make sure that it's the case.

adlr@ next time that this happens, could you please confirm if scrolling with touchpad restores wheel scrolling or not?

I don't need to repro to answer that question! Touchpad scrolling does restore mouse wheel.

Thanks again!

Thanks for the clarification