reinstalling the jami.release.x64.msi client did not help, rebooting the PC did not help.
Deleting the Jami folder from C:\Users\user\AppData\Local did not help.
I found a solution, in AquaSnap I added Hotkey to “Maximize” in “Window management”, and thus maximized the user interface window.
I don’t know what the problem was, but it seems that the Jami window was 0 pixels by 0 pixels. What caused this bug is unknown.