EX3700 disconnects after a while

Brought this to improve my signal in the lounge as my Router (Plusnet HubOne) is in the loft

Initially though it was quite good, connecting via the 5G as the 2G shows amber reception (2G -49, 5G -46, using InSSIDer)

However after a while I got so 'no network' messages

Started Nirsoft PingInfoView with 5 sec ping & logged results. using www.inbox.com as target.

I find that about 1 in 3  pings drops, usually just 1 bit can be up to 3 successive pings.

Then last night, at about 21:00 , complete loss, no connection what so ever.

Connected directly to my router, signal was ~ -59, but could ping www.inbox.com ok

Switched back to the extender 5G link, no internet access (no connection to router either).

Using router connection again, found that I couldn't ping the extender's static address eithet.

After about 3 minutes the laptop switched back to the 5G signal, connection re-established, internet available, but still odd pings being dropped.

Checked Firmware, stated it's most recent

The Phone app suggests the received signal ~ -69 dBm

Any ideas why the drops occur, I notice that  a previous post ( Willff000 Aspirant Aspirant ‎2017-02-27 09:27 AM ) never got an answer, is there any suggestions since then