Both of these need to have their continuation wrapped with (wrap).
I'm honestly a bit fuzzy on why this fixes things but it does.
* 8sync/agenda.scm (%port-request, %port-remove-request):
Adjusted to wrap kont with `wrap' macro.
(make-async-request
(lambda (kont)
(list (make-port-request port port-request-args ...)
- (make-run-request kont #f)))))
+ (make-run-request (wrap kont) #f)))))
(define-syntax-rule (%port-remove-request port)
(make-async-request
(lambda (kont)
(list (make-port-remove-request port)
- (make-run-request kont #f)))))
+ (make-run-request (wrap kont) #f)))))
;; Sugar