Diagnosis
The TV's design has a shallow cavity. Standard 90-degree or bulky HDMI connectors will hit the back panel before seating fully.
How to Fix It
You need right-angle HDMI cables that are specifically designed for low-clearance ports. Buy cables labeled 'low profile' or 'flat 90-degree'. The connector should be no thicker than the cable itself. Connect all necessary cables (HDMI, power, Ethernet) BEFORE you lift the TV onto the wall mount.
If That Didn't Work
For existing cables, you can use slim HDMI couplers/extenders. These are small, straight female-to-male connectors that give you an extra inch of clearance, allowing your regular cable to connect.
Heads Up
Do not force a standard HDMI plug. You can crack the port's internal housing. If a cable doesn't seat smoothly, it's the wrong shape. Test-fit all cables while the TV is still easily accessible, not when it's already on the wall.