Decades ago, i used a small dns host. I wanted to switch a personal site and they just couldn't get the final step of the transfer to work. A ton of "try now" emails spanning several weeks.

Then one day, I was trying to setup MySQL on a personal Linux machine, and it wouldn't let me use my "standard password" for the admin account. I knew I could just use a different one, but I really wanted to know what the problem was. Took a long time, and I don't remember how I figured it out, but I eventually tracked it to the password ending with '!!'.

It took a while to put it together, and I never confirmed with the dns host support it's what fixed the issue but, I changed my password there, tried the transfer again, and it worked without any help from support. I suspect my plaintext password played some part in a script used in the transfer process, and was outputting the previous command in place of the !! I wish I had asked them if that was it, but if it was, they would have to admit to having my plain text password, or lie about it.