Hi Stephanie! Would you be able to share whether these emails are sent out via the Gmail: Send email action or the basic Send email action? If the latter might be applicable here, our team is always glad to check our system for any deliverability issues or confirm successful entries in the email log; please feel free to send me a private message on Community if you'd like us to check into this further for you!
With the Gmail email action, we're not given visibility into deliverability as these are sent directly via the connected Gmail account, but you'd likely have success in checking the Sent folder of your email client directly compared to the automation's run history. If some members of a group are receiving emails and others not, it seems like the recipients might want to check that the sending address is whitelisted for them and that the emails aren't getting sent to an unexpected folder.