So you are doing what I do: using a wifi extender that connects wirelessly to your router, and then running an ethernet cable from the extender to the Teac. I use Netgear routers and extenders, but they probably work similarly.
Usually, these wifi extenders create a new wifi network based off the original wifi network created by the router. So if the original wifi network name from the router is, let’s say, MainNetwork. Then the extended network created by the extender may be something like MainNetwork_ext, or MainNetwork2 or something like that (just to differentiate), but it will typically use the same wifi password as the original. You should try to connect your phone or tablet or other device to the extended network to be sure that the extender is producing a usable network, and even better connect a laptop to the ethernet cable out of the extender just to test that out. Then just be sure that whatever your are controlling the Teac with (phone or tablet) is using the extender wifi network, not the original (so in my hypothetical, make sure the phone or table is connected to wifi network MainNetwork_ext or MainNetwork2 or whatever it is called).
When the Teac is making connection to the network, the display flashes while it is connecting, but when it connects the display stops flashing.
Good luck.
If the extender is NOT producing a solid wifi extended network, you may need to re-pair it with the router, and possibly also establish or validate it with the router software (usually by logging in to a web page associated with your router). It can be a little confusing (the part I’m describing here), but all of this is related to your router/extender interface, and nothing to do with the Teac (the stuff I’m talking about in this post because that is what tripped me up any time I had issues with mine)