[Bug] SPFx WebPart fails to load on Classic Page after May 2025 update

[riadhlakdhar]

Target SharePoint environment

SharePoint Online

What SharePoint development model, framework, SDK or API is this about?

💥 SharePoint Framework

Developer environment

Windows

What browser(s) / client(s) have you tested

• 💥 Internet Explorer
• 💥 Microsoft Edge
• 💥 Google Chrome
• 💥 FireFox
• 💥 Safari
• mobile (iOS/iPadOS)
• mobile (Android)
• not applicable
• other (enter in the "Additional environment details" area below)

Additional environment details

• browser version
• SPFx version 1.20.0
• Node.js version v18.20.5

Describe the bug / error

Since early May 2025, adding a new SPFx WebPart to a classic publishing page in the Pages library of a SharePoint Online site results in a runtime error. Existing classic pages with SPFx WebParts still work, and even the same SPFx WebPart continues to function if it was already present before the issue appeared. However, adding the same WebPart as a new instance on the same page now fails systematically.

Steps to reproduce

Navigate to a classic publishing page (/Pages/yourpage.aspx) in SharePoint Online

Click Edit Page

Try to add a SPFx WebPart (custom or native)

You get the following error on the page:

"Désolé... Nous avons rencontré un problème
Si le problème persiste, contactez l’administrateur du site et communiquez-lui les informations figurant dans la section Détails techniques.
Détails techniques
ERREUR :
Nous ne pouvons pas charger de composant WebPart sur cette page. Utilisez le bouton Précédent du navigateur pour retenter l’action. Si le problème persiste, contactez l’administrateur du site et communiquez-lui les informations figurant dans la section Détails techniques.

PILE DES APPELS :
Error: Nous ne pouvons pas charger de composant WebPart sur cette page. Utilisez le bouton Précédent du navigateur pour retenter l’action. Si le problème persiste, contactez l’administrateur du site et communiquez-lui les informations figurant dans la section Détails techniques.
at d.logClientSideWebPartLoadError (https://res-1.public.onecdn.static.microsoft/files/sp-client/sp-classic-page-assembly_fr-fr_8c1eccd2337952e3111cc7d528705372.js:169:116643)
at https://accor.sharepoint.com/sites/accorlive-rec/talent-culture/Pages/demo.aspx?SPLanguage=en-US:1588:39"

Expected behavior

SPFx WebParts should load and render correctly on classic publishing pages when scripting is enabled.

Actual Behavior

UI displays this error:

"Nous ne pouvons pas charger de composant WebPart sur cette page."

JS console output:
https://res-1.public.onecdn.static.microsoft/files/sp-client/sp-classic-page-assembly_fr-fr_8c1eccd2337952e3111cc7d528705372.js
js
TypeError: Cannot read properties of null (reading 'innerHTML')
at e.convertHtmlToWebPartData (sp-classic-page-assembly_fr-fr_8c1eccd2337952e3111cc7d528705372.js:168:94749)
at d._normalizeWebPartData (sp-classic-page-assembly_fr-fr_8c1eccd2337952e3111cc7d528705372.js:169:117351)
at d.loadWebPart (sp-classic-page-assembly_fr-fr_8c1eccd2337952e3111cc7d528705372.js:169:115167)
at demo.aspx?SPLanguage=en-US:1647:37
js

e.convertHtmlToWebPartData = function(t, n) {
                        var a, i = e._parsingDocument.createElement("div");
                        i.innerHTML = t.trim();
                        var r = i.children[0];
                        if (r && r.hasAttribute(e._webPartAttribute)) {
                            var o = r.getAttribute(e._webPartDataAttribute);
                            if (o && (a = JSON.parse(o)),
                            a) {
                                var s = r.querySelector("[".concat(e._htmlPropertiesAttribute, "]"));
                                **a.serverProcessedContent = e.convertServerProcessedHtmlToData(s.innerHTML, n)**
                            }
                        }
                        return a || void 0
                    }

Tenant: SharePoint Online

Page type: Classic publishing pages in the Pages library

SPFx version: Issue observed across multiple versions (1.20.0)

Custom scripts: Allowed (CustomScriptEnabled = true)

Browsers tested: Chrome, Edge

Additional Context

Bug appeared suddenly around May 3–5, 2025

Suspected cause: recent change in Microsoft’s SharePoint Online frontend, particularly sp-classic-page-assembly_*.js

Likely DOM structure or timing issue (container missing when s.innerHTML is accessed)

Impact
Critical for tenants still using classic publishing pages: cannot insert or test new SPFx WebParts in these pages. Migration to modern pages is not always feasible due to dependencies on legacy publishing features.

[Ashlesha-MSFT]

Hello @riadhlakdhar,
Thank you for bringing this issue to our attention. We will look into it and get back to you shortly.

[shaipetel]

I think might be related to an issue I reported:
#10211

[vikasbansal9888]

Hi @Amey-MSFT / @Ashlesha-MSFT ,

I'm also getting the same error while adding a custom webpart (to display list items) on the SharePoint Online classic page.
However, the same webpart present on existing/old pages are working fine. The OOTB webparts are also working.

The webpart source JS files are not even loading in the browser itself.

SPFx version - v1.9.1
Node version - v10.18.0
Site Template - Publishing site

[riadhlakdhar]

@vikasbansal9888
Can you please check the browser console and send us the error message to make sure that it is the same function (convertHtmlToWebPartData ) that is failing?

[vikasbansal9888]

Hi @riadhlakdhar ,

Please find the chrome browser console error screenshot below:

[riadhlakdhar]

@vikasbansal9888
I confirm that it's the same bug.

[Amey-MSFT]

Hello @riadhlakdhar, @vikasbansal9888,
We were able to reproduce the issue, and we are investigating it. We have logged this as a bug, and our engineering team will look into it.
Thank you!

[saldoc]

Hi @Amey-MSFT ,
Could this issue be related to the recent "SharePoint Online: Content Security Policy Control in Tenant Administration" update? It seems to affect script loading behavior.
Related link: https://www.linkedin.com/pulse/sharepoint-online-content-security-policy-control-van-grondelle-rae5e/

[liyufeng1983]

SharePoint Online: Content Security Policy Control in Tenant Administration

@saldoc @Ashlesha-MSFT @Amey-MSFT
I have 1 question, does the CSP policy impact on the script which is loaded from same domain sharepoint site? the script is hosted in sharepoint Assets library and loaded through SPComponentLoader.loadScript dynamically.

[fahadkhan85]

Hi,

I am also facing the same issue, Old instance of same web part is working fine but new instance is not loading and give same error in classic page. New instance worked in Modern page too.

Did anyone fine the resolution where we can unblock the script load because Allow scripting from active site also did not work.

[Nikkio]

Same Issue here, too bad it's a stopper for a production project that is ready to go-live, an awful situation if you ask me... @Amey-MSFT @Ashlesha-MSFT is there any news on this? Thanks for a kind feedback.

[krisshelly]

Hi,

I'm experiencing the same issue. The existing instance of the SPFx web part works fine on the classic page, but when I add a new instance, it fails to load and shows the same error. Interestingly, the new instance works perfectly on modern pages.

I've already tried enabling scripting using "Allow scripting", but it didn't resolve the issue.
Has anyone found a reliable fix to unblock or allow the script to load correctly on classic pages?

Thanks