Plus sign in usernames - Are there any issues to be aware of?

[Jack Feschuk]

We're currently trying to pin down the cause of users with plus signs in
their user-names not being able to login.

Example user-name: john.smith+group1 at emailemail.com

Are there any known issues with this and FreeRADIUS?
Is the plus sign a "not-safe" character?

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