Check the rotation of the panels in the FPP panel settings. Try changing the settings, then test, change settings then test until you get the right config. Restart FPP after each setting change.
Double check if orientation is looking at the front or back in the setup screen. Also check scan rate. These two are the most common setup errors. It's also possible the scan rate you have is not supported by either FPP or the Pi hat in which case you need a different controller like a Colorlight card.