Hey,
I posted a question about the 'Camera dropped Frame!' message on console log before.
At first I thought this was a hardware issue, but it keeps occuring and my app is not able to detect markers anymore.
But reloading tha scene fixes the issue temporarily, but soon it no longer detects markers again.(about 10 minutes later)
So I do a google search about this issue, and found out that the same message was occured from the OpenCV.
I do use custom OpenCV library on Unity (OpenCVForUnity), but all it does is perspective transformation, Undistortion, etc. It does not control the webcam. And the same project implemented with Vuforia before didn't throw this message.