Authentication Failed with storedKey mismatch even after changing the password

Enterprise demodata_rs [direct: primary] local> db.version()
6.0.11

It started as v4.2 and went through a few upgrades.

This is a 3 node test Rep Set. The user in question was created long ago and, as far as I remember it was working fine, but I haven’t used it in a while. Today I wanted to test something with it but I can’t login, as every time, authentication fails with storedKey mismatch. This password only has letters and numbers and NO special characters. Tbh, I have another user with enough privileges so I can just drop the bad user and re-create it but I wonder if anyone else has seen this before. Any help will be appreciated. Thank you.

This is what the log shows,

{"t":{"$date":"2024-11-01T10:07:53.626-07:00"},"s":"I", "c":"ACCESS", "id":20249, "ctx":"conn25697","msg":"Authentication failed","attr":{"mechanism":"SCRAM-SHA-256","speculative":true,"principalName":"dbabkp","authenticationDatabase":"admin","remote":"127.0.0.1:55914","extraInfo":{},"error":"AuthenticationFailed: SCRAM authentication failed, storedKey mismatch"}}

Things I’ve tried,
I have carefully typed the password many times and I have copy/pasted it, validating it was the right string in the clipboard. I’ve reseted the password in clear text and with passwordPrompt(). I even pasted the same clipboard content for the pwd reset and then for the login, like this,

 Enterprise demodata_rs [direct: primary] admin> db.changeUserPassword("dbabkp",passwordPrompt())
 Enter password
 **********{
   ok: 1,
   '$clusterTime': {
     clusterTime: Timestamp({ t: 1730481257, i: 1 }),
     signature: {
       hash: Binary(Buffer.from("**", "hex"), 0),
       keyId: Long("**")
     }
   },
   operationTime: Timestamp({ t: 1730481257, i: 1 })
 }
 Enterprise demodata_rs [direct: primary] admin> exit
 [eduardo@sandbox01: MongoDB SandBox 1 ~]$ mongosh "mongodb://dbabkp@localhost:27017/?authSource=admin"
 Enter password: **********
 Current Mongosh Log ID: 67250c7935a2baaae2f57183
 Connecting to:          mongodb://<credentials>@localhost:27017/?authSource=admin&directConnection=true&serverSelectionTimeoutMS=2000&appName=mongosh+1.5.4
 MongoServerError: Authentication failed.

Here is the user,

 Enterprise demodata_rs [direct: primary] admin> db.system.users.find({"user":"dbabkp"})
 [
   {
     _id: 'admin.dbabkp',
     user: 'dbabkp',
     db: 'admin',
     credentials: {
       'SCRAM-SHA-1': {
         iterationCount: 10000,
         salt: '**==',
         storedKey: '**=',
         serverKey: '**='
       },
       'SCRAM-SHA-256': {
         iterationCount: 15000,
         salt: '**==',
         storedKey: '**=',
         serverKey: '**='
       }
     },
     roles: [
       { role: 'backup', db: 'admin' },
       { role: 'clusterMonitor', db: 'admin' },
       { role: 'read', db: 'admin' }
     ],
     authenticationRestrictions: [  ],
     userId: UUID("**")
   }
 ]