After resetting the router, formatting the jffs partition and installing the FreshJR QOS script, how do you set up the QOS page?
It should be Adaptive QoS, manual bandwidth (with your ISP limits entered at about 85% for up and down) and the Queue Discipline set to fq_codel.
The order of the categories should be set as per FreshJR's first few posts too.
I would recommend installing amtm to the jffs partition also, and using a spare USB drive, create a swap file for the router to use.
See the link in my signature below for the detailed steps to the amtm Step-by-Step guide to help you set that up properly.
Your router's GUI should not be freezing on you. Let's try to fix that.
Edit: You may also want to install the scMerlin script too if you decide to use a USB drive and install amtm and a swap file. Like my post above shows, it may save you with this very issue you face!