How can I stop a solid state relay from latching up?
One big question is whether this is an AC load or not.  The solid state relay you are using is meant to switch AC loads only and WILL NOT shut off until the zero crossing occurs.

If you are using it for a DC load, then it'll stay on once switched on, and will not turn off until the current goes to 0 (usually at zero crossing with an AC power supply).

If it is an AC load, then you may need to design your snubber more carefully to match your load and power supply. You haven't given us enough information to help you with that part, though.  

If you are trying to switch a DC load, then you need a different type of solid state relay.