Letting you know that MultiplexTransforms only works if all callbacks/defs that point to the same Output are server-side code. If one of the callbacks is a clientside-callback, you get the Duplicate callback outputs error message and the page won’t load.
The project I am working on is quite large/unwieldy, and I am under a tight deadline, so cannot take time away to create a demo. Apologies. But I duplicated the client-side callback with a server-side callback that does the same thing, and was able to comment-out one or the other and produce/remove the error on demand. No doubt about it.
PS - Would it make sense to create either a category or a tag for the Dash Extensions?