Why does Yor call Loid as Loid-san when with others?

Question

I thought it was part of Yor's politeness trope, but this is what ConMan said:

To each other, probably just Loid-san. When I said she would call him anata, I was thinking more in the situations where they need to play up their relationship in front of others, like Yor's brother.

I checked again the 1st episode and indeed Yor does call Loid as Loid-san in front of people.

Guess: Maybe it was a mistake on Yor's part because Yor needed Loid to pretend to be a boyfriend but then Loid made a mistake in the 1st place in saying that Loid was Yor's husband instead?

Or idk is it a common thing in Japan for spouses to call each other -san?

Normally, firstname-san would require some kind of relationship between the speaker and the addressed (e.g. wife and husband).

So ConMan is wrong?

Also I checked S01E08 when Yuri (Yor's brother) actually DOES show up. Yor says explicitly: 'I just call him Loid-san.'

Note: I'm adding the Japan tag based on this, this and this.

Answer 1

It may be partly due to Yor's politeness, but it is perfectly common for a husband and a wife to call each other by first name-san.

According to a poll, it is the second commonest from wife to husband and the commonest from husband to wife. The bold one is FN-san.

Q.家の中で、ご主人のことをどのように呼んでいますか？ (How do you call Husband)　
ニックネーム　39.0％（649名）　
名前にさん・くんなどを付ける　34.8％（579名）　
名前を呼び捨て　14.5％（241名）　
パパ・お父さんなど　4.9％（81名）　
ねい、おい、おまえなど　3.2％（53名）　
あなた　1.2％（20名）　
その他　2.4％（40名）　

Q.家の中で、ご主人にどのように呼ばれていますか？ (How are you called by Husband)
名前にちゃん・さんを付ける　32.2％（536名）
名前を呼び捨て　30.4％（505名）
ニックネーム　27.0％（449名）
ママ・お母さんなど　3.8％（64名）
ねえ、おい、おまえなど　2.8％（47名）
あなた　1.5％（25名）
その他　2.2％（37名）

In Japan, it is legally not (yet) possible for a married couple to have different surnames, so using last name is generally out of question (even though it may happen due to the pre-marriage habit in individual cases). Considering the manga is written in Japanese, using first name-san between Yor and Loid is simply a normal choice.