I had an issue with slider dimmers on three way switches. Next door neighbor is a retired "electrician" from the power company. He jacked it up worse by messing with both switches.
There was no need to open up the other switch as I had left it alone. He couldn't figure it out so my residential electrician friend sorted it out in five minutes.
I do not think I am stupid and can read electrical schematic but the poor excuse for a schematic on 3 way switch packaging is confounding.