We are experiencing the same issue, but in our case it appears to be related to our company name, which contains the character “à”.
The certificate is rejected for the same reason:
Certificate: Sàrl → à = c3 a0
Xcode rule: Sàrl → a + combining accent = 61 cc 80
We are not using Flutter, so I do not believe this issue is Flutter-related.
Topic:
Code Signing
SubTopic:
Certificates, Identifiers & Profiles