This issue is present in 220.127.116.11 as well. Each time the issue occured the device had been online for a long period of time without being accessed. Power cycling the device restored proper login capability.
I did not occur to me to try logging in without a password until I saw your post. Indeed, the switch seems to "forget" the admin account's password in certain circumstances, and looging in as user cisco without a password worked!? Very odd.
If this is how the switch tells me that I have to upgrade the firmware, kudos, very creative.
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