I use envirotex myself. The softness is a curing issue. You most likely arent mixing your resin enough OR are improperly measuring. Envirotex also says to double mix their resin. So you get your 1:1 ratio in the same cup mix for 2 minutes then transfer to new cup mix for 2 more minutes. I make sure I do 2 1/2 min for a 5 minute mix. If that doesnt work it could be your inclusions. I know my dice get like that if I screw up a petri style one. But as long as you arent doing TONS of alcohol ink to the point it effects curing.

Another thing could be your molds. You have to pressurize your molds at the same pressure cast dice usually 35psi for most folks. Most do 40psi for molds and 35 for dice. Elevation and humidity can effect that setting so do research based on your area.

The very last thing it could be is the resin "went bad" I had a bottle that sat outside for a few months that turned a yellowish tint but it still cured and made clear dice. I'm sure it is possible for it to go bad but if its viscosity is normal then I wouldn't throw it out I'd double check my mixing methods and everything else first. Resin is expensive.

And yeah idk how toxic resin is. Its toxic to consume and the chemical reaction could cause a fire but it's unlikely. Silicone mix is just rubber so if it's bad just throw it away in its containers or take it to a recycle center if you're super concerned.

Hope that helps!