Today I tuned a piano where one key activated two hammers.
Upon closer look, I could see that the jack was crooked and positioned a bit under the neighbouring hammer butt.
90% of the time, this is caused by the jack becoming unglued from the whippen.
I decided to remove the whippen and investigate.
First, I removed the bridle strap.
Would you not replace with a slightly larger pin just in case the pin decides to come out again?
You could do that, but this piano had loose pins and I recommended replacing it. Also, it had taken 100 years for that pin to come loose. I don’t imagine it will slip out again for a long time.