Daily report email errors

Hi.. I’ve started to get errors on the daily reports, like this:

[09/Jun/25:00:07:43 +0000] Cannot send email “[NinjaFirewall] Daily Activity Report for xxxxxx” to recipient “xxxxxx”

I have 10+ websites, all with NinjaWP, errors are happening on 2 sites at the moment. Is this a known bug or more likely something conflicting on my sites? I use WP Mail SMTP and Sendgrid, test emails are sending fine.

Thanks