Delay and generation of multiple box when mask detection process is used in a system with thread process

[Mikaelluc]

I'm writing a system to manage multiple cameras on a screen and process each frame detecting missing masks. For that, I use the face detection code from @chandrikadeb7 processing each camera in separated threads. But, when I access the class to make the detections at some point receive an empty frame and crash the process. I put a try-except, as in the first image below, to not crash the whole process and after that, a bunch of random boxes is drawn in the frame, as you can see in the second image below. If someone could help me I'll thank you a lot.

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