@Solla-topee 

I got the following reply from Tp-Link Technical Support: "T5E does not support 5G channels over 100 when the chip is manufactured, so it will lead to the situation you mentioned. I suggest you change the channel to a channel that you can use if you don't have special needs."

If they mean the Intel AX200 chipset on the TX50E cannot use channels like 100 and above due to DFS this https://deviwiki.com/wiki/Intel_Wi-Fi_6_AX200_(AX200NGW) seems to suggest otherwise under Flags "DFS (slave)". Even my ancient TL-WDN4800 seems to have DFS support (http://en.techinfodepot.shoutwiki.com/wiki/TP-LINK_TL-WDN4800) and ran perfectly fine on channel 100. It is my understanding that all Wifi 6 products that support 160Mhz channel width require DFS support in order to work.

I prefer the higher channels like 100 because they seem to provide better signal penetration through walls.

I think a proper explanation of why the TX50E cannot use channel 100 and above is needed as it seems unlikely that the onboard Intel AX200 chipset which is designed for ax 160Mhz channel widths that require as many available channel blocks as possible would have such a limitation.

@Solla-topee 

Unfortunately I am unable to try any channels above 128 as for some reason my router doesn't list them. I am using an ISP (Spark) branded Huawei HG695b ac router with 20/40/80MHz channel widths (https://www.spark.co.nz/help/internet/broadband-help/huawei-hg659b-support).

You can see the router channel list below for an 80MHz channel width:

As you can see transmit power is already at 100%. I do not believe this is an issue with interference as my previous TP-Link wireless N adapter (TL-WDN4800) had no trouble with channel 100 to 128 in the same computer although it uses an Atheros AR9380 chipset and not an Intel AX200. It seems very likely that it is related to DFS as in this region (New Zealand) the DFS band starts from channel 100 as you can see below (taken from the official site https://www.rsm.govt.nz/business-individuals/guidance-for-wisps/).

Although like you say if DFS was unsupported on the TX50E I should not be even able to see my 5GHz wifi on channel 100 which I am able to do and even connect to it although it quickly loses internet and local network access. This makes me instead think it is some issue between the router and adapter relating to the DFS implementation. This could also explain why people have reported issues with the TX50E and 160MHz channel widths (@Kaptain-K https://community.tp-link.com/en/home/forum/topic/261324) as I think in certain countries like the US it is not possible to have a single 160MHz block without hitting DFS channels (unless the router supports the split 80+80 system).

@r1ch4rdNZ 

Hello Everyone,

I currently have a Netgear r6400, which has served me well but seems to have tremendous issues with both of the windows 10 laptops in my household with the 5ghz band. When I'm using either windows 10 laptop(One is an Asus Zenbook, the other is a Dell XPS 13), my 5ghz wifi network seems to have a huge amount of problems.

When I turn the laptop on, it just wont find the 5 ghz network, but will always see my 2.4 ghz network right away. When I check the network list, I see all the other 5 ghz networks that are located in my building but it can take sometimes 3 minutes before my routers 5ghz network will show up. Now when I do finally connect to it, It will periodically disconnect and cant find the network again. This happens on both of the laptops from completely different OEMS. The kicker is that every other device in my house (Apple Tv 4k, Amazon Echo, 2 Iphones, Chromecast, and an Ipad) never have a single issue holding the connection to my 5ghz wifi and it works flawlessly.

@Haucks 

I guess you could try setting the 5Ghz channel manually on the router to 36 in case it was something to do with DFS channels. I know a router that is on certain DFS channels can delay bringing up the 5Ghz wifi for minutes after reboot as it has to scan for active radar etc but I don't think a wifi adapter would need to do so. If the laptops have completely different wifi adapters it seems like the router configuration might be upsetting windows somehow. I have had some wifi issues with windows 10 over the years, not so much with being slow to connect but rather randomly forgetting to connect automatically. Other things you could try are a full network reset (https://www.howtogeek.com/265870/how-to-reset-your-entire-network-in-windows-10-and-start-from-scratch/) or you could set the preferred band to 5Ghz (https://www.tenforums.com/tutorials/151786-how-change-preferred-band-wireless-network-adapter-windows.html).

@Solla-topee Thanks. It isn't a huge issue as I can use the lower channels it just seems very strange.