Hi Lockfand,
TL;DR:
I know, you said purely WoW, but that’s what I thought until really long investigation myself.
If you haven’t yet, open PAINT, select a color for your RMB and draw lines to see if there’s tiny gaps in them. If yes, try the same mouse on a different PC, same procedure. Still gaps, your Mouse is probably done. I bought a new one right now, and my gaps are gone, and so is my problem in WoW.
Long Version:
I recently came back to WoW, and I have the same problem as you have.
I have spent 3-4 hours troubleshooting this yesterday, as I have not had this kind of behaviour happening in any other game so far, only in WoW.
The problem I have (or, hopefully, had) appears like this:
I press RMB to freelook/move while WASDing. The Cursor disappears. Sometimes, it reappears for a fraction of a second, then goes away again and RMB is working again (not releasing of physical button on my mouse). Sometimes, it does NOT reactivate unless I release the button and press it again.
Doesn’t seem like much, but when you are hardwired to play like this and suddenly autoattack critters next to you when you’d be shooting something from afar with frostbolts or the like, it’s infuriating.
Things I have tried:
Swapping the Mouse-Buttons in Windows 10, so the function of my physical buttons is changed. I could play with my left mouse button now like I used to with my right one, but the things I would now do with my physical right mouse button (for example, looking around without turning my character that way) would now show the odd behaviour.
This raised the suspicion that it is a thing that has to do with my mouse and/or OS / Mainboard / USB Devices. Unplugging every other USB device did not solve the problem. Using other USB Ports did neither, neither did using USB 2.0 instead of 3.0 (usually a different USB Controller).
I thought about why I had never had this issue in other games, for example I play a lot of Overwatch, too. I fired up OW, and picked a Hero where I could press RMB for an extended time and actually SEE whether or not the button stopped working. I chose Widowmaker and simply scope in and keep it pressed. After about 30-40 seconds, my scope-in cancelled, I have the same problem in OW but since I usually don’t press RMB for that long a time (mostly 1-3 seconds at best), I probably never noticed it there.
I have tried a lot of other things aswell, for example the DirectX 11 stuff, working around with mouse settings, finding 3(!) mouses apparently plugged into my PC and removing them one by one until my mouse wouldn’t work or I had only 1 left, nothing seemed to work or do the trick, the problem kept appearing and making me insane.
Now, since both games are Blizzard, i had to come up with a way to see if it was my mouse, or Blizzard. I opened up Paint, selected a 2nd color that would draw on RMB, and drew lines. It clearly had gaps in there every now and then.
So, not Blizzards fault: 2 options, my OS / Mainboard is fcked or my Mouse is.
I should have tried it on a different PC right here, but kinda didn’t come up with that on the spot, and instead went out and bought a new mouse today, which does not produce gaps (whew). Remember: If it happens on one device, it’s bad luck. If it happens on two, it might be conincidence. If it happens on three, it’s almost 100% your mouse.
If the problem is NOT your mouse or mice - I’m out of advice here. Probably setting up your OS again, updating BIOS, Drivers etc…
Best of luck to you!