There are a few posts about this cropping up on the Forum.
Firstly I would check the basics, that the AC mode is enabled (AC\N ?) and you are using WPA2 Personal security (AES).
I find it odd that DFS or TPC or any localised interference should prohibit you from changing the channel width setting as at the end of the day it is just a setting. This should not initiate a scan, that is the job of CSMA\CA prior to actually broadcasting on that channel.
The setting allows dynamic changes to the channel width, which should be done dynamically when encountering interference, the setting should just define the parameters.
Its not trivial to make >80Mhz channel width work, due to specific requirements on free channel placement.
Also, most of end-point devices (laptops, tablets, phones, consoles) will not support it anyway, so its useful for backhaul (AP-to-AP) connections mostly.
So I'd say - don't bother about it. It will not give you noticeable speed improvement. Especially with Superhub devices which simply don't have good enough antenna array to provide consistent SNR on wide bonded spectrum.
Most mid/high-end devices support 80Mhz now. If I switch to 40MHz my devices (phone/tablet/laptop etc) connect at 400Mbps but can only reach about 190-200Mbps in speed tests. At 80Mhz they connect at 866Mbps and achieve the full 220Mb on speed tests. I imagine 80MHz is required for customers on 300/350Mbps with typical dual spatial stream devices to have any chance of getting full speed over WiFi.
Had to deal with this recently. Change the channel to a non-DFS number (say 36) and the channel width to 80MHz. Apply. When your internet connection is back refresh the page to make sure it applied (if not, do those steps separately). Then change the channel to your DFS one and apply. Refresh to make sure it applied.
Annoyingly it has to be done in that order or it won't apply. Even more annoyingly, if you restart your router you will have to do all that again as it will reset the channel width to 20MHz.