Posted by I haven’t dug too deep into this one, so what follows may be just coincidental but I thought I would blog it out just in case it happens to anyone else.
While testing AskTOM as part of our Application Express upgrade to version 20.1, I got a bit of a shock when I fired up AskTOM (in a testing environment) after the upgrade. The screen was … well…. “slim”. 
Everything under the banner tabs was missing! A quick look at the underlying page source revealed that all of the usual AskTOM content was indeed there, but it was just not being displayed on screen. I tried the usual things – clearing cookies and caches, different browsers etc, all to no avail. The moment I signed in to AskTOM, the main part of the screen disappeared.
Whilst looking in the browser console area I noticed that my static CDN references were still pointing to the APEX 19 version location. I didn’t think this was the issue, but figured it was something that I should be updating anyway. You can find the static CDN references under User Interface in your application properties.
I updated the reference to https://static.oracle.com/cdn/apex/20.1.0.00.13/ and voila! My AskTOM screens sprang back to life.
Was this definitely the root cause of the problem? I’m not sure. There is more investigating for me to do there. But if you encounter a similar issue during your upgrade testing, make sure you double check that you are using the correct version of your static CDN files.
Note that you can also set your CDN at instance level so that you don’t need to update each application.
Enjoy APEX 20 !
Learning is not a spectator sport 
Hey Connor! Thanks for sharing!
We’re planning our APEX upgrade right now. As far as I know, it’s not supported to import an export file from higher version of APEX into a lower version. At least there is no supported way to do this. Which makes our dev team sad 🙂 And breaks our standard “dev -> test -> prod” routine.
We’re thinking right now how to minimize “non-deploying” period. Maybe you could suggest us something?
Yes, its always a challenge. Lets say you’re going from APEX 19 to 20. I’d be inclined to *retain* the existing APEX 19 for dev => test => prod.
Clone your dev database (or just particular schemas) via DataPump or other mechanism into a fresh database and load APEX 20 into that. Do your regression testing there to gain confidence with the upgraded applications.
Often, its a no-brainer, at which point you’re good to move quickly through Test and Prod. If you do find some necessary changes, or want to take advantage of the new features, or refresh themes etc, then you can opt to do the same in Test.
Ultimately you’ve done a parallel run with both APEX 19 and 20…until such point as you’re ready to bite the bullet and go for Prod.
Thank you!
Hey Connor! Thanks for sharing!
We’re planning our APEX upgrade right now. As far as I know, it’s not supported to import an export file from higher version of APEX into a lower version. At least there is no supported way to do this. Which makes our dev team sad 🙂 And breaks our standard “dev -> test -> prod” routine.
We’re thinking right now how to minimize “non-deploying” period. Maybe you could suggest us something?