There’s a risk involved with any major version update, which is why we always recommend taking a backup!
The first thing to do would be to figure out what is going wrong. I recommend checking your browser’s dev tools console (F12) to see if there are any specific error messages that might point to a module or a specific entity / actor.
We’ve also seen this kind of display issue happening on old / incompatible browsers. Make sure you’re using the newest version of Chrome / FireFox an try to check with a different browser, just in case.
I recommend checking the Bazaar to make sure that your Foundry modules and systems are all up to date. Make sure that your Foundry default version is set to the recommended v10 version, so that your modules can update to compatible versions.
Try launching the world in Safe Configuration to check to see whether the problem still arises. If it does, it might be related to the system / browser / world data rather than modules.
Finally, if none of the above works, you can downgrade Foundry back to v9 and restore a backup of your v9 world, until the problem can be determined.
Hope this helps! Feel free to post screenshots of what you find in your troubleshooting if you get any more info!