Finally, I found out why that function failed for me. It turned out to be a software I used before causing the problem (it deals with keyboard input, so it all makes sense). If it hadn't been for the SDL library update of the game somehow exposing the issue, I could have never noticed it. So, thank you, UnReal World and devs.
That software *hijacked* this key combination and set it to the top priority for itself system wide. Even though I had already uninstalled it long ago, this shortcut key was still not released. Either the software was just poorly programmed, or they coded that intentionally. But anyway, Now I finally found it out and fixed it, along with other problems which the software caused and I just discovered now. Also, a consumer complaint is formed for messing up my system.
Many thanks to you guys for helping me fix the problem in this post!
And if anyone suffers from similar problems, I hope my story can help you or at least provide some thoughts. You can try:
1. Check if mechanical issue.
2. Update or rollback your keyboard drive.
3. Examine your shortcut key registration.
4. Recall if you ever installed something that could mess up the keyboard input.
Hopefully, these methods I once used could help you locate the source of the problem.
I missed the two updates and was playing v3.82 all the time due to this problem. Now I can finally enjoy the game with the new content. But still, it makes me wonder why UrW was not influenced by this problem before while the whole system was.
Computers are tricky little demons after all. And UrW is a magical game made by magical people, I reckon.