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Fix: "Sorry, Something Broke" / Rich Content Editor not populating — caused by Dark Mode browser extensions

VNichols · 2026-08-10T20:04:15+00:00

Symptoms: * Creating a new Announcement (or Discussion) throws Canvas's generic error page: "Sorry, Something Broke." * In Quiz question editors, the Rich Content Editor (RCE) text box doesn't render — instead of the WYSIWYG editor, you just see a stray lowercase "p" where the editor should be. * Happens consistently…

VNichols

Symptoms:

Creating a new Announcement (or Discussion) throws Canvas's generic error page: "Sorry, Something Broke."
In Quiz question editors, the Rich Content Editor (RCE) text box doesn't render — instead of the WYSIWYG editor, you just see a stray lowercase "p" where the editor should be.
Happens consistently across multiple Chromium-based browsers (I hit it in both Chrome and Edge) on the same PC.
Does not happen in Incognito/InPrivate mode, and does not happen on other devices logged into the same account.

Cause:

A third-party "Dark Mode" browser extension (in my case, separate Dark Mode extensions installed independently in both Chrome and Edge). These extensions work by injecting CSS/JS into every page to force a dark theme. Canvas's Rich Content Editor (TinyMCE) runs inside an iframe with its own styling and script initialization, and the injected dark-mode CSS/JS breaks it — either preventing the editor from initializing at all (causing the RCE-dependent Announcement page to crash entirely) or corrupting how it renders (the stray "p").

Because the extension runs on every page, and Incognito/InPrivate mode disables extensions by default, that's a fast way to confirm this is the cause: if Canvas works in Incognito but not in a normal window, check your extensions.

Fix:

Open your browser's extensions page (chrome://extensions or edge://extensions).
Disable extensions one at a time, reloading Canvas after each, until you find the one causing it (for me, it was the Dark Mode extension in each browser).
Once identified, either remove it, or — if your extension supports per-site exceptions — add [yourschool].instructure.com (or your Canvas domain) to its exclusion list so it stays off just for Canvas.
Repeat separately for each browser you use — disabling/removing the extension in one browser has no effect on another, even if both are Chromium-based, since extensions and settings aren't shared across browsers.

Posting this in case anyone else finds their way here searching "Canvas Sorry Something Broke" or "Canvas RCE not populating text box p" — took a while to isolate since it wasn't a Canvas account issue, network issue, or antivirus issue (all of which I ruled out first).

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Jeff_F

Thanks for sharing this. This is a great troubleshooting find and a good reminder that browser extensions can sometimes be the culprit when Canvas behavior appears to be an application issue. The detail about testing in Incognito/InPrivate mode is especially helpful because it provides a quick way to isolate whether the problem is account related, browser related, or extension related.

One additional item that may help is to recommend checking the browser's Developer Tools console (F12) for JavaScript errors after reproducing the issue. While it may not identify the exact extension immediately, errors related to blocked scripts, iframe modifications, or content injection can provide another clue that a browser extension is interfering with Canvas functionality.

It may also be worth noting that similar issues can occur with ad blockers, privacy extensions, script blockers, and accessibility overlays, not just dark mode extensions. If Canvas works properly in an InPrivate/Incognito session but not in a standard browser session, extensions should be one of the first things checked.

dbrace

Indirectly related, this afternoon I worked with an instructor that was not able to access an LTI/app. The reason was because their Google Chrome web browser was set to block third-party cookies. Turned that off and everything worked as expected.

-Doug

Greg

Thanks @VNichols for sharing this. A problem I encounter sometimes is when I'm presenting on something in Canvas and my participants ask about something they see on my screen (my most recent addition is a find/replace Tampermonkey script). They'll ask why they don't see that same button or link, and then I have to remember whether that's a Canvas feature or a third-party tool or script. On my better days I remember to turn off all my scripts, etc.

dbrace

@Greg, for that reason, I have most of my extensions set to be turned off by default but they are set to be enabled "on click". When I want to use them, from the "puzzle piece" icon in the toolbar, I select it and reload the webpage. Then the extension will be enabled like it normally is.

-Doug

RebeccaMcLeish

Thank you so much. This helped me immediately. I turned dark mode off and I can now use the RCE again and effectively do my job without switching browsers. I reached out to Instructure for help, and no solution was provided and they closed the incident. Does this mean I cannot use Darkmode while using Canvas. We do have students that require dark mode.

Although I had already cleared cache and lost valuable search history :(

VNichols

You're welcome I'm glad it helped someone else stuck in the same shoes I was (on the day of my summer final no less). I did the same though and have to reestablish all of my login histories on my personal computer again, it's frustrating! Instructure and our campus Canvas help weren't able to answer or pinpoint a fix for me either, it was just an exhaustive guess and check to see what could be causing it locally. I don't have an answer about Darkmode, but I would guess that there are either other extensions that might do the same thing or maybe Chrome has a native dark mode built in now. My dark mode extensions were several years old and only just caused this problem this summer.

dbrace

Dark mode is something that Instructure/Canvas is working on. It is quite a challenge because of how basically every page, assignment, discussion, and quiz in Canvas is created by instructors, designers, third-party resources (like text-book publishers), and students. Getting all of us/them them to align with how colors are in both light-mode and dark-mode is not easy.

-Doug

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