I'm running 3.3-138 on rt-ac68u and am also facing the same issue. I could not see anything under wireless -> profesional (I am assuming this falls under advanced ->wifi etc.
Looked all through settings & couldn't find anything with USB 3.0 interference listed
I have a SSD on USB 3.0, works fine if attached to usb 2.0
Any assistance at all would be greatly appreciated. TIA to any & all who can help
What is "3.3-138"? This is not a valid firmware version for Asuswrt.