P.S.
If you meet Takeshi Kitano, say Hello to him.

Was it because the code contained hieroglyphs (Japanese characters)?
It seems that the character code is also different.
(My files is UTF-8, yours is Shift-JIS)

I save your plugin and everything is OK. No conflicts.
You can download it here: https://wpgear.xyz/download/1750/
In the plugin description, I replaced the Hieroglyphs with regular English words.

This is self-made plugin to remove 2 bit characters from a post title at the time of posting.
This code contains Japanese.

Code:
https://pastebin.com/0SXA5DvC

An interesting but incomprehensible question. ))
Too little information.

Can you tell me which plugin you have installed?
I would like to try it too, to replicate your problem. Then, I will be able to answer something specific.