Unable to log in with the Rocket.Chat Mac App

Using RC 2.17.7 on Mac OS 10.15.3, I am unable to log in to my work RC server. I get "User not found or incorrect password." However, with the same user ID and pw I am able to log in from a web browser. Also, our sysadmin tells me that there are no logs on the server showing failed login attempts from me. So it seems like something is going wrong inside the app. Or perhaps there is some permissions error with MacOS and the error message is misleading?

I have rebooted, and removed and reinstalled RocketChat.app from the web site (not the App store).

I don't see any error messages in the console when searching for RocketChat (although I do see log entries for the app starting up on log in).

It seems quite possible that this is something wrong with my own usage or installation, since a colleague can use the App successfully against our server, but I don't know how to proceed to try to figure this out without some clue about what is going wrong.

No source file or test is named. Start by reproducing the login failure in Rocket.Chat 2.17.7 on macOS 10.15.3, then inspect the app's console output while connecting to the work server and compare it with the successful browser login. Done means identifying the client-side failure and documenting a reproducible fix or clear cause.