This is a known issue with the Glass layout (Agents Window) in the 3.1.x builds. The fix has been merged and will be included in a future stable update.
In the meantime, you can switch to the Editor layout as a workaround: open Ctrl+Shift+P, search for Toggle Editor Layout, and select it. This should let you access your chats normally.
You can also try reloading the window a couple of times (Ctrl+Shift+P > Reload Window) — in some cases this unsticks the panel.
You may find this related thread helpful: After upgrade, the Agents window is stuck on “Taking a little while”