Originally Posted by P-J
I think you are measuring the values without a load wired into the SSR output. If that is the case, all bets are off in trying to measure anything.
To back up P-J, SSRs switch current, not voltage.
Your light switch turns voltage on & off.
But SSRs are more like a stove top eye control with two settings - full on & very, very low. So low that when your element is connected and the SSR is turned "off" you will measure little or no voltage across the element.
But disconnect the element and you will read a voltage - how much depends in how "off" the SSR really is and your meter's input resistance. Also, there is definitely enough voltage past a "off" SSR to shock you!