Hey CP. I'm Greg, an installation specialist and 9 year Windows MVP, here to help you.
Have you played enough of the erroring files that you know they are solidly intact without glitches and therefore this apprently is not a data loss issue?
If so the best fixes I find for this are here: https://www.techjunkie.com/cant-read-from-the-s...
In addition to testing the external and hard drive with Disk check, I would also test the hard drives surface with diagnostics to know for certain their condition:
https://www.lifewire.com/free-hard-drive-testin...
https://www.groovypost.com/howto/check-hard-dri...
Then I would go over this checklist to make sure the install is set up correctly, optimized for best performance, and any needed repairs get done: http://answers.microsoft.com/en-us/windows/wiki...
Start with Step 4 to turn off Startup freeloaders which can conflict and cause issues, then Step 7 to check for infection the most thorough way, then step 10 to check for damaged System Files. Then continue with the other steps to go over your install most thoroughly.
I hope this helps. Feel free to ask back any questions and let us know how it goes. I will keep working with you until it's resolved.
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