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I'm using a Phidget VINT Hub and a REL1100_0 isolated solid state relay to drive some 5V LED's. To power the LED's (because the relays need external circuit for power), I used the Red+Black wires from a Phidget cable attached to my VINT Hub (Red wire --> LED+ | LED- --> relay port | relay GND --> Black wire).

I have the VINT Hub plugged into USB on my Macbook, and using the Phidget Control Panel I switch the LED on and off. After ~20 switches, the LED suddenly stops turning on. I try with another LED in the same port and it's repeatable. Leaving the LED steadily on does not cause it to burn out, and doing this switching thing using one of the VINT ports on the Hub directly does not cause it to burn out. Also, the internal PWM switching (e.g. at 90% duty cycle) on the relay doesn't burn the LEDs out. It only happens from manually toggling the relay open/closed.

Any idea why this is happening? Would it be better to use a different Phidget for this purpose?

//Thank you for reading

If you're powering the LED directly from the VINT Hub's 5V pin you should also have a resistor in series to limit the current to the forward current specified on the LED's data sheet. You don't need to do this when using the VINT port in DigitalOutput mode because there is already an internal resistor in the VINT Hub's circuitry.