Lucidchart Import Chrome Plugin not working

[jfiore-pg]

Preflight Checklist

• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for a feature request that matches the one I want to file, without success.

Potentially related issue, but the guidance in here did not solve it: #5496

Describe the bug
The app.diagrams. page keeps telling me to install the plugin (even though I already installed it). (see screenshot with devtools open)

I have already installed the plugin and accepted its permission request. (See screenshot)

I also made sure that Third-Party Cookies are enabled and even explicitly added the domains that the extension needs.

I am successfully logged into Lucidcharts in the same browser in a different tab.

Chrome Version: 145.0.7632.117 (Official Build) (arm64)

Console Errors:

import.html:30 Refused to apply style from 'https://app.diagrams.net/tools/lucid/mxgraph/css/common.css' because its MIME type ('text/html') is not a supported stylesheet MIME type, and strict MIME checking is enabled.Understand this error

import.html:1 Unchecked runtime.lastError: The message port closed before a response was received.

To Reproduce
Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior
I expect it to not prompt me to install the plugin and find the Lucidchart diagrams to export/import.

Screenshots
See above

draw.io version (In the Help->About menu of the draw.io editor):
Not sure.

• draw.io version x.y.z

Desktop (please complete the following information):

• OS: Max OS (Arm)
• Browser: Chrome
• Browser Version: 145.0.7632.117 (Official Build) (arm64)

I tested the problem in incognito/private mode with all browser extensions switched off, write "yes" below:

• No. That wouldn't work.

[draw-io-triage-bot]

👋 Thank you for opening this issue!

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Summary: The user cannot use the Lucidchart Import Chrome extension with app.diagrams.net — the page keeps prompting them to install the plugin even though it's already installed. This is very likely the same third-party cookie/cross-origin authentication issue resolved in #5496, despite the user having added some cookie exceptions.

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💡 Possible Solution Found

We found a potentially relevant solution in a previous issue:

This issue is very likely caused by Chrome's third-party cookie blocking behavior, similar to what was resolved in #5496 with Brave browser. In #5496, the user resolved the issue by lowering their browser's shields/cookie protections. Even though you've added some cookie exceptions, Chrome 145 may still be blocking the cross-origin authentication flow between diagrams.net and lucid.app. Try the following: (1) Temporarily disable all third-party cookie blocking entirely in Chrome settings (not just adding exceptions), (2) Ensure that both app.diagrams.net and lucid.app (and subdomains like api.lucid.co) are fully allowed for cookies, (3) Try using a fresh Chrome profile with default settings to rule out any extensions or custom configurations interfering. The Unchecked runtime.lastError: The message port closed before a response was received console error suggests the extension's messaging channel is being interrupted, which is consistent with cookie/storage access issues preventing the cross-origin handshake. The CSS MIME type error (common.css returning text/html) was also noted in #5496 and appears to be a separate known issue on the diagrams.net side (likely a missing file returning an HTML 404 page).

📎 Source: #5496

Please check if this addresses your issue. If not, let us know what's different about your situation.

🔍 Possible Related Issues

This issue might be related to existing issues:

🔴 #5496 - Lucidchart import broken
Same symptom (Lucidchart import not working), same console errors (CSS MIME type error, runtime.lastError), and the root cause in #5496 was third-party cookie blocking by the browser — which is very likely the same issue here despite the user's attempts to whitelist domains.

Please check if any of these address your issue. If this is a duplicate, we may close this issue and continue the conversation there.

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_{🤖 This is an automated response to help with initial triage. A human maintainer will review this issue. If you've provided all the requested information, no further action is needed - we'll get back to you soon!}

[jfiore-pg]

I also tried it on a different computer (Windows 10 with Chrome Version 146.0.7680.80 (Official Build) (64-bit))

In this one, it doesn't prompt for me to install the plugin, but it shows nothing.
See screenshot:

[jfiore-pg]

I also tried a fresh Chrome profile where the only installed extension is the draw.io extension.
Also verified that Third-party cookies are allowed.
Same result:

[jfiore-pg]

If it is helpful, I'm logging in with my Google Account (not username/password) because that is what I'm required to do by my organizational policy.