Here is a question regarding the whistle sound. (I think I know the answer to this.)
Could you have a different whistle sound in the engine compared to the tender given there is two separate sound boards and main control boards with these not receiving the same identical signal from the remote?
I believe this is what happens and it is somewhat repeatable.
I started a different thread documenting problems I found with my Triplex. I was able to get two different (non-complementary) whistle sounds, one from the engine and the other from the tender. As stated, a simple reset synced up the correct whistle combo. (That's a good thing.)