Fixed.

Oh so I checked and it seems that my edits are not the reason for the error. But it needs to be fixed anyway, I will take care of this.

Oh that's because I removed one character from the alphabet and didnt adjust the sampling function. I will fix this.

Sorry for the problem.

(OP is talking about JavaScript)
I can confirm the issue, there is an off-by-one error in the RNG:

let characters = "abcdefghijklmnopqrstuvwqyzABCDEFGHIJKLAMNOPQRSTUVWXYZ0123456789!@#$%^&*()-_+={}[]|\:;?/>.<,)";
// characters.length === 91
...
random += characters[Math.round(Math.random() * 91)]
// worst-case scenario: random += characters[91] i.e. undefined

This is my fault. I forgot that parseInt takes a second parameter which completely changes the behavior. It should be fixed now.