I just tested it here and could not duplicate your problem. However, my test environment is very different from yours. Please provide more detailed information so that we can check the problem further:
(1) Open Windows Task Manager and tell us the CPU and RAM usage percentage. The laptop is very low-powered. If the CPU or RAM usage is too high, then it could cause this problem. In this case, you can lower your video resolution and frame rate.
(2) In VSS, hover your mouse on top of one working camera, click Stop to stop it. Wait for one minute and let us know if the 3rd camera can connect.
(3) Start the camera again in VSS; then launch another webcam program such as Skype, try to access the webcam in Skype by clicking Tools --> Options --> Video Settings; select the webcam that does not work in VSS, and let us know if Skype can access the webcam and display the video. If not, please stop the webcam in VSS first, then retry it in Skype. If Skype still cannot access that webcam, then it is unlikely to be a VSS problem.
(4) If you have another computer (hopefully a more powerful computer), please test it on that computer and let us know if it works fine.
I think most likely it is a problem of your PC being too slow (AMD C-50 is a very old and slow CPU. You can try a lower video resolution and frame rate), or a problem with the webcam, or the USB hub does not have enough power for 3 webcams.