Is a comma after Johor required?

If Johor is a location, then, yes, it should be followed by a comma.

Thanks, Roberta.

Johor is a location.

It's a state in Malaysia.

Thanks.

I had to google it myself. Initially I thought it might be in Algeria, lots of unrest there at the moment.

So, actually, I think this is wrong, but this comma rule is a pain in the ass.

The comma rule in place is the Comma Used to Set Off Non-essential Words or Phrases. The problem in some cases is it’s up for debate which phrases or words are essential to the meaning of the sentence.

Like this:
Essential: The sixth-century philosopher Boethius was arrested, tortured, and bludgeoned to death. (word)

Nonessential: Company managers, seeking higher profits, hired temporary workers to replace full-time staff. (phrase)

Essential: The person checking tickets at the counter asked for a form of identification. (phrase)

Nonessential: My uncle, who is eighty years old, walks three miles every day. (clause)

Essential: The woman who interviewed you is my sister. (clause)

Source:
https://owl.purdue.edu/owl/general_writing/punctuation/commas/commas_with_nonessential_elements.html

Riot police have been called in at the Ayer Hiram results centre, Johor on Wednesday evening.

If you think the specific name of the Ayer Hiram results center must be named so that you know exactly what location you’re talking about, no commas around; if you think any idiot should be aware that the AH results center is widely known as Johor, set it off on both sides by commas.