I had the same problem when I bought a RT-AC66U a few months ago.
The problem diappeared when I entered the router's IP address in a white list in ESET NOD32, and also in a white list for Java script (accessed through Windows Control panel).
I'm not sure if white listing in Java will help you in this case, but I mention it just in case it helps you or someone else in future.
PolarBear
The problem diappeared when I entered the router's IP address in a white list in ESET NOD32, and also in a white list for Java script (accessed through Windows Control panel).
I'm not sure if white listing in Java will help you in this case, but I mention it just in case it helps you or someone else in future.
PolarBear