Outlook 2019 keeps asking for older user email credentials yet no Account listed on PC, AD, or Exchg

(Exchange copy 2010 i think:) So we keep getting a popup asking for J****B****@*******.org, when the user is L****G***@*******.org. This is a nonprofit account, and outlook version is 2019 License on Windows 10 Pro, Dell Latitude only about 2-3 years old. The system is setup to where Active directory changes mirror over to exchange, but on both J****B****@*******.org does not exist, L****G***@*******.org has no aliases, and there are no added accounts in outlook, the local machine, AD or otherwise, yet the popup keeps asking for J****B****@*******.org password, and it says "outlook" at the top just like when a password is changed and outlook has to have you reinput those credentials.

We have gone over everything i know how, all i can think of creatively is maybe a data file is user specific? something having to do with transferred or archived emails? but again i see no aliases on anything.