Upgrading from Mendix 8.18 to 9.24.29 is a major jump and includes important changes in the React version used by the client, the Atlas UI framework, and client-side caching behavior.
If some pages are failing to load in Test and UAT environments while others still work, the issue is usually related to stale client resources, Atlas UI compatibility, or outdated widgets/modules, rather than the container size itself.
First, I would recommend doing a clean rebuild. When moving from Mendix 8 to Mendix 9, the compiled JavaScript and CSS bundles change structure, and older build artifacts can sometimes remain in the deployment directory.
In Studio Pro, go to App → Clean Deployment Directory, run the application locally once, then create a new deployment package and redeploy it to Test/UAT. This helps ensure the app is rebuilt with the correct Mendix 9 client resources.
Next, check Atlas UI compatibility. Mendix 9 introduced Atlas UI 3, so if the application still contains older Atlas UI resources from Mendix 8, some UI components may fail to render correctly.
Open one of the failing pages and inspect the browser console (F12). If you see JavaScript or React-related errors, update the Atlas_UI_Resources module from the Marketplace to a version compatible with Mendix 9, then rebuild and redeploy.
I would also verify all Marketplace widgets and modules used on the failing pages. Older modules built for Mendix 8 are a common cause of page load issues after upgrading to Mendix 9. In particular, check modules such as Community Commons, Encryption, Excel Importer/Exporter, and any custom UI widgets. Also review the Error List in Studio Pro for deprecation or compatibility warnings.
Since the problem happens in Test and UAT, it is also important to review the runtime logs and metrics in those environments. Look for CRITICAL or ERROR messages at the exact time the page fails to load. If the runtime is hitting memory limits, you may also see signs of restarts or Out Of Memory behavior in the environment metrics.
So overall, I would focus on these steps in this order: clean the deployment directory, redeploy with a fresh package, update Atlas UI resources, update Marketplace modules, and then check browser console and runtime logs for page-specific errors.
Although the environment is using an S21-STANDARD container, that would not usually explain why only specific pages fail. If the issue is page-specific, it is much more likely related to client compatibility or widget/module issues introduced during the upgrade.
If this resolves your issue, please mark the answer as accepted so it can help others facing the same problem.
Hi Vijaya,
When I was upgrading from Mendix 8 to Mendix 9, I found the migration documentation really useful.
https://docs.mendix.com/refguide9/moving-from-8-to-9/
There are a lot of changes between Mendix 8 and 9, so do take some time to read this if you haven't already.
In your situation, pay particular attention to upgrading widgets and Atlas, as these affect how your pages are displayed.
https://docs.mendix.com/refguide9/moving-from-8-to-9/#upgrade-widgets
https://docs.mendix.com/refguide9/moving-from-8-to-9/#updating-atlas-module-optional
The good news is that the migration from Mendix 9 to 10 is far easier when you get to that stage.
I hope these links help. Good luck!
Hi,
When upgrading from Mendix 8 → Mendix 9, issues like pages not loading are usually not related to the container size. In most cases it is caused by outdated modules or widgets that were compatible with Mendix 8 but not fully compatible with Mendix 9.
A few things I would check first.
1. Update Marketplace modules and widgets
After upgrading to 9.24.29 you should update all major modules that interact with the UI or runtime, for example:
Older versions of these modules from Mendix 8 often cause pages to fail silently in Mendix 9.
Go to Marketplace → Update modules and make sure you are using versions compatible with Mendix 9.
2. Check the browser console
If a page is not loading, open the browser developer tools and check the Console tab. Most upgrade issues appear there as:
This usually tells you exactly which widget or module is causing the page to fail.
3. Check logs in the environment
Look at the Runtime logs (especially Client and Widget log nodes). If a widget fails to initialize, Mendix usually logs something like:
Widget could not be initialized
or a JavaScript error referencing the widget.
4. Clear the deployment and cache
After a major upgrade it is also a good idea to:
Old client resources sometimes cause pages not to load properly.
5. Verify deprecated widgets
Some widgets used in Mendix 8 (especially custom widgets or older DataGrid widgets) are no longer supported the same way in Mendix 9 and must be replaced with newer versions.
From experience, when pages fail to load after an 8 → 9 upgrade, the root cause is almost always an outdated widget or Marketplace module, not the container size. Updating those modules and checking the browser console usually identifies the problem quickly.