The bounce rate of what, exactly?
Because the bounce rate of Hide My Email addresses being deliverable is going to rise over time, by design.
Whenever I start getting spam at an address that's been leaked, I deactivate it. I've done the same with my oldest gmail account, but the work required there is notably higher.
If they were moved to plain old icloud.com, I could absolutely see a bunch of companies starting to filter out all icloud.com email addresses to avoid private relay. Either just because they’re jerks or from bounce issues.
Keeping it on a subdomain fixes that problem, to some degree. If the user is named [email protected] no one is going to think that’s a real address. It’s very obviously a private one. So it’s not like they were “camouflaged.“
It’s a little odd they’re switching the subdomain though.