[C#] General issue: CodeQL scanner encounters issues without reporting them

**Description of the issue**

I set up CodeQL scanning using default configurations in a private repository. When scanning the C# code, it reports that it had a low quality scan due to issues, and recommends resolving those issues. However, when I check the status page there are no other issues reported.

Looking at the actions logs reveals the same situation:

```
CodeQL scanned 630 out of 630 C# files in this invocation. Check the status page for overall coverage information: https://github.com/**********/********/security/code-scanning/tools/CodeQL/status/
Analysis produced the following diagnostic information:
##[group]C# analysis with build-mode 'none' completed (1 result)
* C# analysis with build-mode 'none' completed.
##[endgroup]
##[group]Low C# analysis quality (1 result)
* Scanning C# code completed successfully, but the scan encountered issues. This may be caused by problems identifying dependencies or use of generated source code, among other reasons -- see other CodeQL diagnostics reported on the CodeQL status page for more details of possible causes. Addressing these warnings is advisable to avoid false-positive or missing results. If they cannot be addressed, consider scanning C# using either the `autobuild` or `manual` [build modes](https://docs.github.com/en/code-security/code-scanning/creating-an-advanced-setup-for-code-scanning/codeql-code-scanning-for-compiled-languages#comparison-of-the-build-modes).
##[endgroup]
##[group]C# was extracted with build-mode set to 'none' (1 result)
* C# was extracted with build-mode set to 'none'. This means that all C# source in the working directory will be scanned, with build tools, such as NuGet and dotnet CLIs, only contributing information about external dependencies.
##[endgroup]

##[group]Uploading code scanning results
```

There doesn't seem to be any information in the output showing what the issues it encountered were or how to fix them.

Start by reproducing the default CodeQL scan for C# with build-mode 'none' and compare the Actions logs with the code-scanning status page. Investigate why the low-quality-scan diagnostic does not expose the underlying issues or remediation details. Done means the encountered issues are reported with actionable information, or the behavior is documented as expected.

索引モデルが issue の本文から書いたものです。