TEAC NT-505 impossible connecting to WiFi router o such LAN: help me please?

Do a factory reset (easy to do), then download the 1.21 firmware and install it.

https://teac.jp/int/product/nt-505/download

I didn’t even know v1.22 existed because on the Teac Europe site they don’t have 1.22, just 1.21.
Wonder why that would be? That’s why initially when you guys started talking about 1.22 I didn’t understand what you were talking about.

in the year I’ve owned mine I never visited the Japan site, only Europe and was always thinking I was current with v1.21. 

Now if you really want to be sure you are getting the version that’s worked great for me, pull 1.21 from the Europe site and skip the Japan site. How bizarre would that be if there were slight differences? Ugh, probably overthinking it ... But still odd to me that EP site no mention of 1.22

Update: Installed v1.21, did number of resets, and nothing really worked. Well there was a lesson learned of course and that was my unit is definitely hosed in a way I can’t explain, but can easily guess its HW related.

My lastest experiments show if I connect it over USB to say my Mac it would always be able to get an IP and be available over the network (go figure). However, if I do leave it to Network mode and power it down, and keep it down for say 10-15 mins and then power up (doesn’t make any diff if HW power switch or remote button) it would not get an IP.
All-in-all it’s going back to Teac (Onkyo here in US). A bit disappointing I was the one of the few unlucky Teac users out there cause according to Onkyo, there are no other reports of such behavior, or don’t want to admit it.
Although might be tempting... stay on v1.21 if you ask me and don’t fix something is not broken :)

I just received my NT 505 yesterday afternoon that I purchased from TEAC direct via *bay (am I allowed to name them?). Once I started the unit up the HR Streamer app prompted me to update the networking firmware to version 11.6c which I did without a hitch. I checked and my unit has the version 1.10 I/F firmware. My unit was automatically recognized by Roon and everything went perfect from there. 

I did follow a link in Roon for the unit that took me to TEAC's EU site where I found a link to upgrade the I/F firmware to 1.21. In looking at the release notes for v1.21 it states that it added "Roon Ready" to the unit. Since mine was already doing that I see no need to upgrade. One thing I did note is that the firmware installation instructions say to upgrade the network firmware before upgrading the I/F firmware.

I only got a couple of hours of playtime with mine but so far I really like it. It's sound is much smoother than the ESS 9018 that is in my Bluesound Vault 2i and the ESS 9038 in my two channel amp. I got it as primarily a headphone DAC/AMP though I am feeding it's single ended outputs to my 2 channel system (Arcam SA 20 amp). The specs say that the headphone amp section max power is only 500mW x 2 so I also bought a used SPL Phonitor amp here on A'gon and it should get here tomorrow or Friday. That should really help out with any hard to drive phones I may (will) acquire in the future.

Since I took the 4 port switch out of the chain, mine has been working perfectly.  Still waiting for my new router, but I think the switch was the problem in my case, not the NT-505.  Let's hope I don't jinx myself now!