Hello, welcome to Doom9's forum!
I probably can't help you with the problem. Sometimes frame drops occur because of video quality, such as switching from a quality broadcast signal to an old video tape signal. Sometimes they occur because of background tasks, such as antivirus software, doing something special. And, since you've already researched your problem, it probably isn't one of those two reasons.
But I can offer advice that will make it more likely that people with more knowledge may read this thread. I recommend editing your post and changing the title to something more descriptive.
"Puzzled???" may be how you feel, but it's not a good description of the problem. Many of our members won't read posts if the discussion isn't in their area of expertise, and that's ok. But many of our members skip right past posts if the discussion has a nebulous title, also. It's why
Rule #9 exists.