Some files cant be scanned? I would like to know why

Hi, When i run a thorough scan with archives enabled it goes up to around 170,00 files but when its done it says that a lot of files could not be scanned, is this normal?
Thanks, Bill

Welcome to the forum.
It’s a subject that’s been discussed many times and reveals many answers in the search function.
Here is just on of the threads which contains the answer to your question.