That's precisely the issue you're facing. SendGrid's unsubscribe mechanism is designed to make sure you don't email people who tell you to stop e-mailing them, so it stops any e-mails being sent out to them for other purposes if you don't use unsubscribe groups. By using their default unsubscribe without groups, you effectively told SendGrid "block e-mails to the people that unsubscribed so they don't get spammed."
SendGrid, without groups, has no idea what you're sending. It can't tell the difference between your newsletter and password reset e-mails. It just knows dualipavsbritney420@gmail.com said I don't want e-mails from this sender, and effectively stops those e-mails from being delivered wholesale.
To fix this, you probably want to create a newsletter specific group and a group for "important site communication" that would be things that IPS sends out by default. Then, manually move your unsubscribes into the newsletter group (that's probably what they wanted when they did it).
See here to set it all up: https://app.sendgrid.com/suppressions/advanced_suppression_manager
Look here on how you should update your e-mails: https://sendgrid.com/docs/ui/sending-email/index-suppressions/
Ideally though, you'd want to remove these e-mails from your actual tool that sends out Newsletters instead of having SendGrid manage suppressions. Each e-mail that is suppressed consumes one of your e-mail credits, so it's probably better to go in and remove them from your mailing list.
What do you use to send newsletters? IPS itself or some third party product/application?