Can you access & play the problem tracks in a regular mp3 player program? It may be that your external hard drive is failing first off. If they play ok then read on . . .
Seeing as you have scoured already for answers or clues and drawn a blank rather struggle on bite the bullet and start from scratch. Rebuild the whole operating system on the laptop from a new installation (not an over the top install), install traktor, and async the entire contents of your music library all over again. Allocate your hard drive the next available drive letter in the chain of drives on your system, this is only a personal preference as this just keeps your drives in order. Do not change the drive letter after async’ing all your tracks. Should the problem exist after all this at least you will have that task ticked off. At the moment you are in limbo with a system that isn’t working and there is this option you can take. I do feel confident this will sort this problem and realise it is a drastic measure. The most labourious part I guess is async’ing all your tracks if you have a large library but it is just a waiting game. Good luck 🙂
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