Hi, I had the same problem and went through difficult time with corporate IT even to get listened at ( as this is not the official emal client app)
I use Aqua mail to manage and sync my Exchange company email account from my mobile. It works beautifully.
The problem arise every time (quarterly) the Company system requires me to change the Exchange account password.
After that, I update the account password onto the mobile device, and that's when the problem start.
The error 401 comes intermittently and randomly, with frequent blocks of my account on the company system, arguably for security reasons ( the sytem feels external abnormal attempt to connect to the exchange account).
I assume that the mobile Android system keep stored somewhere the old password which creates a conflict and hence either the error on the app, or the block of my company laptop account. Interestingly, the blockage or the error 401 disappear without doing nothing after some hours( I wasn't able to record times or isolate events) but than they come back.
The reason why I assume that is this while trying to fix the issue, I also installed an Android/OS sytem update which came available from the mobile manufacturer ( oneplus). Also I have deleted the account from Aqua, and reinstalled after the OS system upgrade.
I have done nothing intentionally to fix the issue, but after the sytem upgrade, the Exchange account is working and it's been doing that steadily for the last few hours.
Any idea where this hidden old password could be stored? Please note that before this session, I cleaned the phone cached data and the problem persisted, so should be something else.