Registration emails not going to admin

I have Ultimate Member installed on a website for a client.

The client tells me that, recently, no new member signup notifications have been coming to the company email address.

I have made a test membership and nothing is received at the client’s email address.

However, I have reset Ultimate member to send to my work address, created a test membership and got the notification email at once.

Does anybody know why that might be happening? I am using the plain UM without premium features, plus the UM reCAPTCHA plugin.

Thanks!