@alexmiller I was able to find the reported error (outside of the generator). The last s/def below fails with the following error:
1. Unhandled java.lang.AssertionError
Assert failed: (every? (fn* [p1__18963#] (not (select?
p1__18963#))) unq-specs)
impl.clj: 423 clojure.alpha.spec.impl/schema-impl
(s/def :foo/bar
(s/schema {:a/b string? :b keyword?}))
(s/def :foo/baz
(s/select :foo/bar [:a/b]))
(s/def :foo/buz
(s/schema
{:z :foo/baz}))