INP issue in processing duration

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Fabio Cazzavillan

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May 12, 2025, 10:05:31 AM May 12
to web-vitals-feedback
Hello everyone!

Happy to share my first message here. Over the past month, I’ve learned a lot while trying to fix my (mainly) INP-related issues, and today I’d like to share one that I find particularly curious.

Page affected : https://www.mutuionline.it/guide-mutui/calcolo-rata-mutuo.asp
Issue : High INP on mobile (267ms today), based on real user PageSpeed data.

How to reproduce :

Tested on a real high-end Android device (not reproducible via Chrome emulation — a ~20x CPU slowdown seems necessary to reach similar values).
Tap inside the first input field on the page.
Delete one character.
The INP issue should appear.

I’ve attached a stack trace that highlights the problem.

What’s puzzling:
The delay seems to occur during the "processing duration" phase, but as far as I can tell from the trace, nothing significant is happening — no long tasks, LoAFs, or repaints. I’m really not sure where to look next.

Thanks in advance for any suggestions!
Fabio
mutuionline-case1.json

Michal Mocny

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May 12, 2025, 10:36:40 AM May 12
to Fabio Cazzavillan, web-vitals-feedback
I agree that this looks incorrect.  There are two distinct interactions, both of which do produce a paint update (you can see in screenshots), yet the first set of event timings for the first interaction appear to not get included in that first paint.

Because this is a great repro case-- would you mind filing a bug over at crbug.com (add to componentid:1456231, and you can look for examples in  this hotlist )?

Cheers,

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Fabio Cazzavillan

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May 15, 2025, 7:07:58 AM May 15
to web-vitals-feedback
Hello,


Thank you!

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