I'm stuck at the "Checking System..." screen

I can’t get past the “Checking System…” screen, the loading bar keeps moving as if it was really loading, but nothing happens. I’ve tried reinstalling the program many times as well as restarting the PC, but none of these worked for me. Does anyone have a solution to this issue?

This just started to happen here, out of the blue.
Restarted LbF for it to recognize SSL errors after changing a site’s domain,
and now it’s stuck at «Checking System».

Console shows a mysterious error:
nw_path_close_fd Failed to close guarded necp fd 44 [9: Bad file descriptor]

Update: restarting the MacBook fixed this.