@Adam2021 

Getting the exact same thing; started a few days ago.  No answers yet I'm afraid.  Reset the router, resat the cables, re-paired the devices; nothing. I thought it may have been a recent Windows 10 update, but I have an old laptop still running Windows 7, and that too can't find the network anymore.  The WiFi in the room I'm working in is a bit unstable hence buying several of these adapters.

@Adam2021 

Eventually got mine working.  Downloaded the tpPLC utility, and then ran a firmware update whilst connected to one of the devices (I have 4), then ran around the house pairing 1 to 2, 2 to 3, 3 to 4 (making sure it had done the job on one before pairing the next).  Can't say it'll work for you - and as a non-technician I often find I can't explain why it suddenly works again! - but it did the trick for me.  Good luck.