When you open a terminal in plasma you are effectively launching Konsole App which then loads a profile using and executes commands in a pre-defined shell - which can be bash, zsh, fish or any other shell.
So your problem may be the the profile used by Konsole.
Even though you cannot type anything - you should be able to access Konsole Settings menu. The shortcut - hotkeys - to open is CtrlShift,
From there you can change the profile - the default breath uses zsh.