• Tested on Windows 10 and Server 2019:
• .NET 4.7:
• Microsoft.ML (1.5.2)
• Microsoft.ML.LightGbm (1.5.2)
• LightGbm (3.0.0)

Issue
It crashes in this line

• var model = pipeline.Fit(trainData);

• I get this error: System.InvalidOperationException: 'LightGBM Error, code is -1, error message is 'Unknown importance type: only support split=0 and gain=1'.'

This error can be reproduced by an example. I just used the example in docs.microsoft.com and able to reproduce it.

https://docs.microsoft.com/en-us/dotnet/api/microsoft.ml.lightgbmextensions.lightgbm?view=ml-dotnet

I created a console app and you can access it from the link below:

https://drive.google.com/drive/folders/1-wc04CM75-IGoxjRAniDuhqI-zrHTWwM?usp=sharing

I talked to the LightGBM team and they mentioned this issue exists in .Net code and not theirs. This is the third time this issue has been reported (#5431 and #5382) and each time it has been closed without any resolution.