[Support request] Featured image causes large LCP in one site and not in another site

[Vranjes]

This issue is related to my previous two, it seems I have to submit it as a separate topic. I have four sites with the same theme and same plugins, but for this case I shall use two as examples.

1. In one site (site 1) LCP is fine, tested many times and it is usually as in the screenshot:

https://paste.pics/784b344e368e4158b2d86f10dbcd48ab

2. In other site, LCP is large (red), checked for various posts, no difference. So in Core Web Vitals I have that all URLs need improvement.

3. But when I remove featured image in site 2, the result is always good (green).

I created a test site of site 2, exact copy, for testing, URL is given below. So even when I disable all plugins, no improvement as long as featured image is there. It does not matter the size of the image, tried with 600, 800 pixels, etc.

4. I take the featured image from site 1, and use it as a featured image in site 2 and in the test site. LCP is red, see the screenshot:

https://paste.pics/acd41bd1b92217c0343062db06feb28d

Below I give both URLs. Can you please see anything in ‘View Page Source’? What makes the difference between two sites? My hosting support could not help. I can give you login data if you are willing to check.

[Fernando]

Hi Vranjes,

The two reported issues are:

1. Reduce Initial Server Response time – This is something you should speak to your host about.
2. Reduce Unused JS – The one causing this is Google Tag Resources. It’s well known that Google Tag is very heavy for a site’s performance. We don’t like recommending lots of plugins but you can try serving the GTAG scripts yourself with this one: https://wordpress.org/plugins/host-analyticsjs-local/

[Vranjes]

Hi
thank you for the prompt reply.

1. This is about two sites at the same hosting, same configuration. One has issues and the other not. Can you elaborate, what to say to my hosting in view of this? I have already spent a day with them yesterday.

2. Again, the same configuration on two sites. So what makes the difference between them?
Thanks

[David]

Hi there,

the two sites are not identical, for example the second site with the higher LCP is loading Google Tag Manger and pinterest JS.

Neither of which are present on the first site.

GTM, like the majority of Google assets is known to affect load performance.
And any JS that is affecting the LCPs HTML such as pinterest may also adversely affect the LCP timings.

[Vranjes]

You are right, one is completely new and without those extras added. Can you suggest any tool to deal with these things? Would WP Rocket help?
Thanks.

[David]

Plugins like perfmatters and wp rocket can defer loading of scripts such as Pinterest.

The GTM, there are some plugins that allow you to host it locally ( Perfmatters is one ) .

[Vranjes]

Many thanks.

[David]

You’re welcome

[Author]

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