Hey, thanks for the report. This looks like a known issue: the @ file picker doesn’t always pick up newly created or recently changed files until you reload the window. That’s why it can find CASE-CASE2.md which you didn’t touch, but not case1 and case3.
Quick fix: open the Command Palette with Cmd+Shift+P or Ctrl+Shift+P and run Developer: Reload Window. After that, recently changed files should show up in @ again.
If it still can’t find them after a reload, check that the files aren’t being excluded by .cursorignore or .gitignore. Since case2 is visible, it’s probably not that.