I am not receiving verification codes from one sender, but only when I use Firefox on my Macbook.
In the past I have received verification codes from my bank when sent via text message to my iPhone, which then forwards them to my Macbook. But today, I did not receive those codes on my Macbook even thought they were sent to my iPhone. Furthermore, when I used Safari, I received the codes on my Macbook, but not when I used Firefox. So the issue is not my iPhone failing to relay messages to my computer, but only its failure to do so when I use Firefox.