Probably a keymapping issue (hotkeys?).

So, just started this game, bug appeared in the prologue. Noticed this bug after finding springberry - I couldn't select Calisca with "2" button, it would select my main instead. Having another party member join me in the cave didn't help. Recruiting new members in Guilded Vale after the solo part didn't help either - second party slot cannot be selected with a keyboard.

Possible trigger might have been when I accidently wacked Calisca with my sword, and after that the other way around. Reloading doesn't help, however, new game does.

Will provide save if necessary,

Hey there!  The number keys are actually re-bindable selection groups.  You may have accidentally rebound the '2' selection group to your main.  Try selecting Calisca and then pressing Ctrl+2 to set the group.

Thanks! That helped=)