Does anybody in tech support read these forums, or is this just a big waste of time?

Your firmware is too old. Try the latest firmware TL-WA854RE(EU)_V1_140827 from http://www.tp-link.com/en/download/TL-WA854RE_V1.html#Firmware

Also, if you connect directly to the router instead of the range extender, will the same problem occurred? If not it is not caused by the range extender. You may check whether there is some firmware for your router.

Note: this is a user forum. You can submit a ticket to get technical support via http://ticket.tp-link.com/index.php?/Tickets/Submit

Hi there. Thanks for the reply.

This is what I get upon trying that file:

Error code: 18005

Upgrade unsuccessfully because the version of the upgraded file was incorrect. Please check the file name.

Filename of the direct download: wa854rev1_en_3_14_8_up_boot(140827).bin

The main router works fine. It's just out of range for the most part.

Cheers

Your model is WA850RE or WA854RE indeed?
Try to download the latest firmware for the right model.
http://www.tplink.com/en/download/TL-WA850RE_V1.html#Firmware
After download it, unzip it and try to upgrade again. :)

OK found the right version. I didn't see that it was the wrong model. Cheers

It seems it is still happening, even with updated proper firmware. Still testing.

In the meantime, any advice?

Cheers

Facetime Audio drops for 10 seconds every 4 to 5 minutes, and sometimes doesn't come back up again, and I have to call back.

Your phone is iPhone 6?
Except the above issue, any other problems to access internet by WA850RE?
In main router's Wi-Fi range, no problem at all?

my iPad is iPad Mini. No other problems. I'm completely within range. One floor above my main router, full signal.

How is it going now? My friend helped me to test by iPhone 6 and 6+ and we called each other but no problem at all.
What's the MAC OS of your iPad Mini? Any other apple devices you can test in your case? Facetime Audio drops when you call someone? If some one call you, does it drop as well on your iPad Mini?

Update:
Out of curiosity, I tried my brother's iPad Mini version 8.1.2(12B440) but no problem at all. :)Maybe you should update your iPad Mini. Anyway, if there is any update on your side, pls report it here.