Hey hey! Thanks for playing :3
The ending for completing the puzzle should trigger automatically upon successful puzzle completion, so that's odd. It always triggered when I played through each version to test it. Are you hearing a sound after inputting the last character of the code that sounds like a sorta 'correct' sound effect, rather than a 'wrong' sound effect?
It shouldn't send you to any other ending because completing the puzzle successfully should automatically lock you in to 1 particular ending with no way out besides reloading an older save.
To help me find out what's going on, other than the question I already asked, could you please let me know the following:
Are you playing the male voices or female voices version?
Which voice did you select for your playthrough out of voice 1 and voice 2?
When you finish inputting the code for the puzzle, what is the first line that your partner says to you?
Are you putting the '!' character at the end of the code?
Extra question:
Beneath a spoilers header or just emailing me at melancholicmarionette@gmail.com could you give me a brief description of what happened in the endings you've seen already?
Hopefully, with that info, I should be able to figure out what's going on :3 Hope you enjoy the rest of your weekend!