I think I have the same problem here (Debian Buster with R 3.5.2).
Everything was fine till 2 days ago.
Then rsconnect stops and tells me that I need to update the package (don't remember the exact message).
I update to 1.0.2.
Now both showProperties() and showLogs() give a "! Couldn't find any deployments matching supplied criteria."
applications(), accounts() and accountInfo() show the right information, token included.