[racket] Typed Racket Predicate Generation Regression?

Been awhile as this is old library code, but I recall the below code once
worked for me.  Currently failing at the moment, though may have broken at
any time of the last few months.

#lang typed/racket/base

(define js-null 'JsNull)

(define-type JsNull 'JsNull)
(define-predicate JsNull? JsNull)

(define-type Json (Rec Json (U String Boolean JsNull Number (Listof Json)
(HashTable Symbol Json))))

(define-type JsObject (HashTable Symbol Json))
(define-predicate JsObject? JsObject)
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