Can't edit QoS policy on R6050 router

I'm trying to change the QoS priority of one of my devices connected to my router, but when I select the device from the QoS Priority Rule list and click the edit button I get a generic browser error message. I've tried it on multiple devices and using different web browsers but I just get different error messages. On Firefox I get "The connection was reset", on Edge I get "Hmm... cannot reach this page", and on Chrome I get "routerlogin.com didn't send any data". No matter what MAC address whose policy I try to edit I get these errors, but if I manually add a priority rule then I can edit it freely. I'm running Windows 10 and both my OS and the router are fully updated. What can I do to update my device's QoS priority?