I consulted this issue with tp support before. it supports to V2 by default and use UDP161. They have no community name. For security settings, try to look for one in public library.

When it loses connection, is your main router still working properly? How about just restart your main router? does it get tplink work again? try to update the latest FW for tp.

i don't think so. they are different unit.

only C9 V4 US support. if yours is EU, then it doesn't support.

bob2017 wrote Same problem here. Login page is very slow and the 2.4 ghz is off line. Everything was working great until I upgraded. Any fix for this or do I have to return this router? Not clear...

i don't know what names you are talking. But i know we change the network/media server name in the web interface. And it looks that we are not able to change drive name as there is no place saying...