[C1sc0cat]

It used to and maybe still does cause problems with how google parsed robots.txt files!

Which is why all my robots.txt files have a comment on the first line.

[Someone1234]

> Which is why all my robots.txt files have a comment on the first line.

That doesn't stop a BOM being generated or consumed.

[YSFEJ4SWJUVU6]

BOM is only a problem with strict syntaxes, which robots.txt is not an example of. If the "consumer" simply ignores invalid or meaningless lines, you can avoid issues from invisible characters by not having anything meaningful on the first line of your file.