Terminal tmux - Problem

I upgraded my debian server from stretch to buster without problems, but c9 doesn’t open the terminal for me.

I get the following error:

tmux: loadlocale.c:129: _nl_intern_locale_data: Assertion `cnt < (sizeof (_nl_value_type_LC_TIME) / sizeof (_nl_value_type_LC_TIME[0]))’ failed.

I tried

  • Check locales, and changing the local LC_TIME to different types and I can’t make it work.
  • TMux out of c9 runs smoothly, But I think c9 uses an internal one.

Can you think of anything?
Thank you!