Given these two statements I wanted to suggest something completely out of left field, and my apologies if this doesn’t make much sense but given the amount of troubleshooting you’ve already done I figured it was worth a shot.
If the disconnections are specific to your PC and seem to only happen while moving, it’s possible that they are occurring due to a keyboard issue. I have seen certain keyboards cause disconnection issues in WoW specifically while moving (holding W or W+another movement key for example).
Without getting too deep into why this happens with WoW, the gidst of it is this: Some keyboards, whether through their firmware or software, are set up so that if you hold down a key like W the game will register multiple key presses per second instead of a single held down W key. So instead of WoW seeing “W key down”, (hold), “W key up” the game sees “WWWWWWWWWWWWWW”. Those rapid inputs may cause a disconnect. This behavior is usually caused by key repeat rate functions on the keyboard (like a rapid / turbo mode) where it increases the repeat rate beyond the default.
A simple test for this issue would be to borrow a different keyboard from another system, plug it in, and play test the game while in a raid where the issue happens most often.
Again my apologies if this is totally off base, but since I have seen (a very odd) issue like this in the past I thought I would mention it. If that doesn’t turn out to be the issue, well that is one more thing to check off the list!