Thanks for replying - answers below
What FW version are you using?
DIR-882 HW:A1 FW:1.20
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What browser are you using?
tried multiple - chrome, edge, firefox
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Be sure to clear all browser caches before entering into the routers web page.
always
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Has a factory reset been performed and setup from scratch?
no - as this just masks the issue, its not a solution - if users have to do a factory wipe before they can use functionality, then its a bug.
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Update:
1. I took a chance and upgraded to 1.3 security beta
That immediately fixed the save issue, was able to change QoS settings.
But the download speed dropped to 50 - ouch (slow up too)
2. waited 12 hours including couple of restarts and speed stayed way low.
3. downgraded to 1.2 firmware
speeds went immediately back up to over 500
and QoS settings remained the same as what I had set under 1.3
So - some serious bugs there but i'm leaving it as is now, don't want to risk breaking it more