But the dimmers themselves don’t have a connection to neutral? They need a power supply to run their circuitry, and while they can play games with ground or the load wires, those don’t always work well, especially non-linear loads like LED bulbs. One thing you might try is to temporarily put an incandescent bulb or two in the circuit to change the load.
Not all LED bulbs are dimmable, and not all dimmers can handle LED bulbs, and not all dimmers that (say they) can handle LEDs are compatible with LED bulbs that (say they) are dimmable, especially when the dimmers don’t have a neutral connection.