The search in admin in article list works only if I use Latin characters or numbers.
Every time I use my language (hebrew) I do not get any result (just the all article list).
This bug is only in the latest version (2.7.1) and went over the settings but nothing worked.

Is there a way to fix it ?

Hello Eran,

Please install the 2.7.2 DEV version
github.com/getk2/k2

still in 'dev' ? Is it stable? I'm dealing with live sites (cannot afford any beta/unstable extensions)

It is stable and you can use it live sites.
To be 110% sure you can always backup and revert should anything (highly unlikely) goes wrong.