Global variable with gtkmm

I created a gtkmm app and a custom c++ class. In this class i have a static member and I must initialize it first as a global variable but by initializing global variables I get the following runtime errors when the app starts:

(process:33366): Gtk-CRITICAL **: 23:12:00.041: _gtk_style_provider_private_get_settings: assertion 'GTK_IS_STYLE_PROVIDER_PRIVATE (provider)' failed

(process:33366): Gtk-CRITICAL **: 23:12:00.041: _gtk_style_provider_private_get_settings: assertion 'GTK_IS_STYLE_PROVIDER_PRIVATE (provider)' failed

(process:33366): Gtk-CRITICAL **: 23:12:00.041: _gtk_style_provider_private_get_settings: assertion 'GTK_IS_STYLE_PROVIDER_PRIVATE (provider)' failed
Segmentation fault (core dumped)

Any idea of how to tackle this?