You won't get ozone in the tub on high because ozone is set up to shut off when you touch any of the buttons for safty. You are not suppose to breathe it.
It sounds as if the check valve is sticking still, or possibly in backwards or maybe a kink in the line somewhere. If this is the case it needs to be addressed so you do not burn up your new ozone chip. Personally I would run a whole new ozone line with new check valve to set if this works. Fairly easy to do.