All of this sounds odd, Bentonite is usually pretty effective if you
hydrate it properly.

That said, if I had to guess I think the sterile filter pulled out
nutrients too and you just need to get some in there. If I am doing 5
gallons of sparkling wine usually just hydrate one pack of EC1118 and
that is all I need. Try warming it a bit if it's under 75F and
stirring it to add a little oxygen too.

Joe