Experience Builder brings 'Blank Page' ExB v12.1

[aperi]

Hi all,

I have a base ArcGIS Enterprise 12.1 single machine deployment (Portal, Server, and Data Store on one box). The Portal home page, Map Viewer, and Content all load normally, but when I launch Experience Builder from the app launcher (https://<machine>/portal/apps/experiencebuilder/), the page comes up completely blank. No error message, no spinner, just an empty screen that stays stuck.

What I've tried so far:
- Cleared browser cache and tested in an incognito window and a second browser: same result
- Confirmed the rest of Portal is healthy 
Environment:
- ArcGIS Enterprise 12.1, single machine base deployment
- Accessing through the Web Adaptor, currently over HTTP (not yet on HTTPS with a CA-signed cert)

Has anyone else hit a blank Experience Builder page on 12.1? Wondering if this is a known issue with the release, or a resource failing to load. Any pointers on which logs or configs to check would be much appreciated.

Screenshot of the blank page is attached.

Thanks!

[Ke_Xu]

Hi @aperi,

What error do you see in the browser console? Does the same issue occur when creating other apps, such as an Instant App?

Thanks,

Ke

[davidround]

Yes. Blank screen when launching any experience or template from experience builder. Looking in dev tools it's failing to load some javascript stuff. I can't fix it 😞

[Ke_Xu]

 @davidround, could you please capture the error messages from the browser console? Also, please submit a Support ticket for this issue. Thanks.

[davidround]

Sure. I have opened a support ticket because I am no further along. 

Issue:

ArcGIS Enterprise 12.1 (upgraded from 11.4) Experience Builder is failing for all users. The builder loads but throws client-side JavaScript errors including "Cannot read properties of undefined (reading 'WebMap')" and "Initializing theme manager failed - Cannot read properties of null (reading 'default')", preventing normal use of Experience Builder.

To troubleshoot, I have:

• Tested in multiple browsers including InPrivate mode.
• Tested with a newly created Portal user.
• Performed a Portal for ArcGIS repair installation.
• Installed the latest available Portal 12.1 patch (Portal for ArcGIS Security 2026 Update 2 Patch).
• Verified Portal is healthy and returning Web Map content successfully through the REST API.
• Verified helper services and federation appear healthy.
• Checked Portal logs but no corresponding errors are generated when the issue occurs.

The issue affects all users and appears to occur within Experience Builder itself rather than a specific experience. It occurs whenever creating a new experience, loading a template or opening an existing experience.

[O_Kantarcioglu_ct]

Hi,

I have the exact issue.

I have installed ArcGIS Enterprise 12.1 with Enterprise Builder and when I open the Experience Builder, I see a black screen and nothing comes up on Developer Tools except in console "Load module error. TypeError: can't access property "WebMap", G.ItemTypes is undefined"

I have a working 12.1 deployment on which I installed the components individually and have no issue there.

When I compare the size of both folder in each environments I see that working environment has 400 Mb folder size and the broken environment has 336 MB folder size. 

Please let me know how it turns out @aperi 

Thanks!

[davidround]

I have a support ticket to investigate the issue but this might be helpful information @Ke_Xu if the file sizes are different.