Join returns duplicate values

I was porting an existing .NET code to .NET core.

There is a specific join code that is not working in EFCore. The code is :

var values = (from config in tblConfig
                               join info in tblInfo on config.No equals info.No
                               where (
                                     //some conditions
                                     )
                               select config).ToList();

In EFCore this returns a collection where most of the data are duplicated. Especially, there is a column regNo which in some cases are "-1". This value is duplicated in all the rows after the join.

I tried the grouping, removing the conditions etc as mentioned in some other post. But didn't work. I am pointing this column since it is easy to understand.

Config Table

Info Table

Based on the No field I need to join. It seems all the empty cells replaced with non-empty content from same table.