I got a snail and algae eater yesterday and both have already died.
There is something else going on with a PH of 8.5 ammonia becomes super toxic. At pH 8.5, only 0.17 ppm is considered lethal to inhabitants.
I cant see a high PH killing a mystery snail.
I keep Mystery snails in a tank with Bumblebee Gobys PH 8.4 and its hard as rock and my snails love it. And yes strangely the Gobys leave the snails alone, I guess they are to busy hunting Endler fry.