Reproduction steps:
1. Open the “My project” Project
2. Open the “Assets/Scenes/SampleScene.unity” Scene
3. Open the “Assets/Scripts/AnySystem.cs” Script and observe lines 29-30
4. Observe the Console Window

Expected result: No error is displayed in the Console Window
Actual result: An error is displayed in the Console WIndow

Reproducible with: 0.51.1-preview.32 (2021.3.17f1)
Could not test with:

• 0.51.1-preview.21 (2020.3.44f1 (error CS0619: 'FixedString128' is obsolete: 'Renamed to FixedString128Bytes (UnityUpgradable) -> FixedString128Bytes'))
• 0.17.0-preview.42 (2021.3.17f1 (error CS8377: The type 'U' must be a non-nullable value type, along with all fields at any level of nesting, in order to use it as parameter 'T' in the generic type or method 'NativeList<T>'))
• 1.0.0-pre.15 (2023.1.0a26 various Library/PackageCache/com.unity.collections@2.1.0-pre.6 errors)

Reproduced on: Intel MacOS 13.1

Notes:

• if you comment the line 29 and call and return it through a separate method (uncomment line 30), the issue does not occur.
• The issue does not occur in the OnUpdate() function