@Kevin_Z Had no issues since installing the AC1750 and not needed the extra TL-WA855RE that was past return date. Cheers, Mark

@Kevin_Z I've purchased a tp-link AC1750 Range Extender............ will be sending back 1 of the TL-WA855RE to Amazon, the other is outside its return period so looks like will need to swallow that...

Well this morning I was on 2nd floor, checked with my tablet and both the tp-link extenders could not be connected to....... both showing authentication failure. But able to connect to main router in...

@Kevin_Z I'm still having connection failures, seems to be authentication failures. Only way to resolve seems to be power recycle. I have various fixed devices (cameras and smart plugs/switches) then...

After firmware upgrade I notice that by default the extenders were both set up to be a DHCP server..... both from same IP range as main router..... so think what likely happened was a clash of IP's...

Noticed there is a newer Firmware (TL-WA855RE(US)_V4_191213) so upgrading both units. Will see if this helps