I just tried changing my email on studentaid.gov to a simplelogin alias (using SL is a habit at this point) and I got notifications that emails from it were bounced while trying to verify the email change with sent codes. I looked it up and found a bunch of Reddit posts about issues with SL and iCloud.
I had one but most likely it was spam (domain is from a job site). Other than that, no other issues between SL and iCloud.