*+Description+*
We have an issue where AssetDatabase.LoadAssetAtPath is returning null when trying to get a subasset / child asset of an asset in OnEnable.

We have a workaround by using AssetDatabase.LoadAllAssetsAtPath, but this seems like a dirty workaround and it brought confusion and errors multiple times now, as even today someone changed it to the single AssetDatabase.LoadAssetAtPath not realising the issue and I had to find they did that and revert it back.

This is also mentioned in the forums and various places by users
https://discussions.unity.com/t/loadassetatpath-returns-null-after-compiling/865875

*+Initial setup+*
6000.0.16f1+
You can use our package to repro it, specifically on this branch:
https://github.cds.internal.unity3d.com/unity/com.unity.ai.designer-monorepo/tree/feature/blackboard-asset-group

If you import the 2 packages in the repo from disk.

*+Reproduction steps+*

1. Setup the packages from the branch (feature/blackboard-asset-group) in the repo linked above.
2. Inside BehaviorAuthoringBlackboardAsset.cs, find the method GetOrCreateBlackboardAsset. Replace LoadAllAssetsAtPath with AssetDatabase.LoadAssetAtPath<RuntimeBlackboardAsset>
3. In the package manager, import "Unity Behavior Example".
4. Find Example Behavior Graph.asset and expand it in the project window to see its subassets

*+Expected behaviour+*
(Describe in as much detail as possible what you expect to see happen, ideally with examples, screenshots, links, and logs.)
There should only be a single RuntimeBlackboardAsset child asset in the mentioned asset. Also, the AssetDatabase.LoadAssetAtPath shouldn't be null if there is already a subasset.

*+Actual behavior+*
(Describe in as much detail as possible what is actually happening, ideally with logs, screenshots, links etc.)
AssetDatabase.LoadAssetAtPath inside GetOrCreateBlackboardAsset returns null even if the asset already exists, when it's called from OnEnable.

This causes our system to create another subasset and add it to the asset, and you'll see there are multiple subassets of the same type now.

*+Logs and Links+*
(Add links to Yamato jobs, links to logs, and add a stack trace in this section)