TFS not tracking changes if items added manually and not included into vs2015 solution

I've added a folder with asp.net core project which isn't supported by Visual Studio 2015 (which is used for everything else) and thus not included to the general solution. To have those files in source control I had to manually add them using "add items to folder" command in source explorer. So they are checked-in but tfs not tracking changes for them anymore although there are differences that are shown if compare to the latest folder on the server:

How do I make TFS track them and show pending changes for edited files?

According to your description, looks like these files are all out side of Visual Studio.

Not sure if you are using server workspace or local workspace.

When adding or editing the workspace you click Advanced >> . There is a setting of Location: Local/Server.

For local workspace, when your script or anything else changes files outside Visual Studio, your workspace detects the changes automatically.

It also detects adds or deletes but you have to include them to your Pending Changes manually with the link under Excluded Changes.

For server workspace, you could choose to use Reconcile command. See https://stackoverflow.com/a/22860674/932282 for a complete answer.

Besides, you could also take a look at other solutions in below similar question:

• How to have TFS 2010 detect changes done to files outside of Visual Studio?
• Force TFS to detect changes