I am having issues with my Asus RT AC3100 when enabled bandwidth limiter. It blocks internet completely for all the guests. I wanted to set 1mb for both upload and download. I'm using latest firmware 384.13.
Is this a dirty upgrade to 384.13_0 or did you do a full reset to factory defaults after flashing the latest RMerlin firmware?
You may want to see the M&M Config and possibly the Nuclear Reset guides in the link in my signature below to get your router back to a good/known state.