Mobile Core Web Vitals Issue

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Mobile Core Web Vitals Issue

thetitan72

12:26 pm on Jan 24, 2025 (gmt 0)

Hi,

Since mid-December, Google has downgraded my mobile pages, citing: "CLS issue: more than 0.1 (mobile)."

I’ve tried everything I can think of—checking image loading, optimizing caches, adjusting CSS, and more—but after two reviews from Google, the issue still hasn’t been resolved. I’m at a loss as to why this is happening. For desktop/web, everything works perfectly fine.

Does anyone have any insights into what might be causing this?

[edited by: not2easy at 12:41 pm (utc) on Jan 24, 2025]
[edit reason] Please see TOS [webmasterworld.com] [/edit]

not2easy

1:04 pm on Jan 24, 2025 (gmt 0)

Content Layout Shift (CLS) happens when the resizing for mobile is not properly resizing the content of the page so the content appears differently on Mobile and desktop. Since Google switched importance of mobile efficiency several years ago, they consider layout shift as an important defect because it changes where they might want to show ads.

It is CSS where you would look to correct the problem. Most browsers let you view the page on a desktop device as if it were a mobile device, that can help you visualize what needs work and where to fix it.

Wilburforce

1:47 pm on Jan 24, 2025 (gmt 0)

CLS also happens where loading of some page content (e.g. images) is deferred: when the content loads it displaces what was already loaded. Also (obviously?), it happens where loading of CSS is deferred.

It doesn't help that CSS is treated as a render-blocking resource in online speed-tests, which advise deferring it. Don't.

Best is loading resources in the order the user encounters them, and CSS is first-paint.

Martin Potter

2:00 am on Jan 25, 2025 (gmt 0)

and CSS is first-paint.

I should have already figured this out, but how does one ensure that the CSS loads first (or early), or perhaps ensure that it does not load late?

not2easy

2:46 am on Jan 25, 2025 (gmt 0)

You can use in-line CSS for anything critical so that it loads with the element/s that most urgently need it. For most sites it is not necessary, but if there are specific instances of elements that are being affected, that is one way to ensure it is managed.

Wilburforce

3:44 pm on Jan 25, 2025 (gmt 0)

how does one ensure that the CSS loads first

By loading it in the <head> section of your page e.g.:

<link rel="stylesheet" type="text/css" href="https://www.example.com/stylesheet.css">

That way it loads before the content. Generally, put

1. Styles that apply to the whole site in a separate stylesheet, and load it as above.
2. Styles that apply to only one page in <style></style> tags in the <head> section of that page.
3. Styles that apply to only one item inline.

Loading a separate stylesheet before content falls foul of most online speed tests (e.g. "Avoid chaining critical requests" in pagespeed), but even a fairly extensive stylesheet isn't more than a few KB, and online tests make no allowance for that fact that the stylesheet can be cached (so is only loaded for the first page a user views).

Martin Potter

12:43 am on Jan 26, 2025 (gmt 0)

Thanks, @not2easy - I don't use in-line CSS so ... oh, wait, there is one page with one instance of in-line CSS, but that is all.

And thanks too @Wilburforce - My style sheet is loaded in the <head> section and it is only 13 kB (still with lots of stuff that could be taken out now). So I guess that my situation is all right.

Thanks to both of you for very informative answers.

NickMNS

5:07 pm on Jan 26, 2025 (gmt 0)

Does anyone have any insights into what might be causing this?

Page speed insights, or Lighthouse in Google Chrome dev tools will tell you exactly what the problem is. In page speed insight, halfway down the page there is a "Diagnostic" section where there are links,

Show audits relevant to: All FCP LCP TBT CLS

Click on "CLS" and it will show exactly what is causing the problem.

Gagan_Kumar

12:10 pm on Feb 11, 2025 (gmt 0)

If Google flagged your mobile pages for CLS issues (more than 0.1), try these fixes:

Set Image & Video Dimensions – Always define width and height to prevent layout shifts.
Reserve Space for Ads & Embeds – Allocate fixed space to avoid sudden movement.
Optimize Font Loading – Use
```
font-display: swap;
```
to prevent invisible text.
Manage Dynamic Content – Ensure pop-ups or banners don’t push content around.
Use CSS Transform for Animations – Avoid animations that change layout size.
Test with Real Users – Use Chrome User Experience Report (CrUX) for real-world data.

Aim for a CLS score below 0.1 for a smooth, user-friendly experience. If issues persist, audit your site for hidden layout shifts.