No RADIUS errors in /var/log/secure when this is happening?
Wondering if this failure is due to the Blast RADIUS fixes being enabled now, what does show aaa radius-servers require-message-authenticator say?
Edit: Any special characters in the login name? sk183201: After an upgrade to R81.20 Jumbo Hotfix Accumulator Take 96 and higher, users with special...
Also there was a major update of the Gaia kernel from 3.10 to 4.10 so that may be related as well.
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