I observed the crashes with SDL 2.0.9 in an application that opens multiple audio devices, but it might still happen with the current version (although less likely).

If two threads manage to enter SDL_DBus_Init at the same time and both get past the LoadDBusLibrary line, the first thread that fails to connect to the session bus will clear the function pointers in the dbus structure by calling SDL_DBus_Quit. This might cause the other thread to crash when it still needs to call some of these functions.

I was hit by this bug since by default there is no system bus in Flatpak environments and 2.0.9 still failed when the system bus is not available. D-Bus was accessed in my case because each opened audio device gets its own thread and each of these threads tries to raise its priority by asking rtkit over D-Bus.

How about wrapping SDL_DBus_Init in a mutex?