Thanks for the additional information. I assume you are using Enterprise with IWA SSO authentication.
If so, this is a known issue when using non-Windows devices, such as Android and iOS devices. The sign in session gets cached in the login webview, so once the user signs out, and you try to sign back in, the cached credentials are used. We are working on fixing this issue in the internal browser and will have an update for you once we make progress.
Glad I found this. We have Fire crews using iPads which don't use our O365 logins used throughout the City, but our AGOL site is using O365 and we have seen this issue where the previous user is still logged in. I will be curious to hear the resolution and any possible work arounds for now.
There is currently no update on this issue and it is unlikely to be resolved for the upcoming release, and requires further changes in the underlying AppStudio framework version.